Typescript definition is broken if @types/express-ws is in the same package.json

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When @types/express-ws (`npm install --save-dev @types/express-ws`) is added to the same Typescript project that uses websocket-stream, `tsc` produces the following:
```
> tsc

node_modules/websocket-stream/index.d.ts:13:5 - error TS2416: Property 'on' in type 'Server' is not assignable to the same property in base type 'Server'.
Type '{ (event: "connection", cb: (this: Server, socket: WebSocket, request: IncomingMessage) => void): this; (event: "error", cb: (this: WebSocket, error: Error) => void): this; (event: "headers", cb: (this: WebSocket, headers: string[], request: IncomingMessage) => void): this; (event: "listening", cb: (this: WebSocket) => void): this; (event: "stream", cb: (this: WebSocket, stream: WebSocketDuplex, request: IncomingMessage) => void): this; (event: string | symbol, listener: (this: WebSocket, ...args: any[]) => void): this; }' is not assignable to type '{ (event: "connection", cb: (this: Server, socket: WebSocket, request: IncomingMessage) => void): this; (event: "error", cb: (this: Server, error: Error) => void): this; (event: "headers", cb: (this: Server, headers: string[], request: IncomingMessage) => void): this; (event: "close" | "listening", cb: (this: Server) => void): this; (event: string | symbol, listener: (this: Server, ...args: any[]) => void): this; }'.
Types of parameters 'event' and 'event' are incompatible.
Type '"error"' is not assignable to type '"connection"'.

13 on(event: 'connection', cb: (this: WebSocket.Server, socket: WebSocket, request: http.IncomingMessage) => void): this;
~~

node_modules/websocket-stream/index.d.ts:14:5 - error TS2416: Property 'on' in type 'Server' is not assignable to the same property in base type 'Server'.
Type '{ (event: "connection", cb: (this: Server, socket: WebSocket, request: IncomingMessage) => void): this; (event: "error", cb: (this: WebSocket, error: Error) => void): this; (event: "headers", cb: (this: WebSocket, headers: string[], request: IncomingMessage) => void): this; (event: "listening", cb: (this: WebSocket) => void): this; (event: "stream", cb: (this: WebSocket, stream: WebSocketDuplex, request: IncomingMessage) => void): this; (event: string | symbol, listener: (this: WebSocket, ...args: any[]) => void): this; }' is not assignable to type '{ (event: "connection", cb: (this: Server, socket: WebSocket, request: IncomingMessage) => void): this; (event: "error", cb: (this: Server, error: Error) => void): this; (event: "headers", cb: (this: Server, headers: string[], request: IncomingMessage) => void): this; (event: "close" | "listening", cb: (this: Server) => void): this; (event: string | symbol, listener: (this: Server, ...args: any[]) => void): this; }'.

14 on(event: 'error', cb: (this: WebSocket, error: Error) => void): this;
~~

node_modules/websocket-stream/index.d.ts:15:5 - error TS2416: Property 'on' in type 'Server' is not assignable to the same property in base type 'Server'.
Type '{ (event: "connection", cb: (this: Server, socket: WebSocket, request: IncomingMessage) => void): this; (event: "error", cb: (this: WebSocket, error: Error) => void): this; (event: "headers", cb: (this: WebSocket, headers: string[], request: IncomingMessage) => void): this; (event: "listening", cb: (this: WebSocket) => void): this; (event: "stream", cb: (this: WebSocket, stream: WebSocketDuplex, request: IncomingMessage) => void): this; (event: string | symbol, listener: (this: WebSocket, ...args: any[]) => void): this; }' is not assignable to type '{ (event: "connection", cb: (this: Server, socket: WebSocket, request: IncomingMessage) => void): this; (event: "error", cb: (this: Server, error: Error) => void): this; (event: "headers", cb: (this: Server, headers: string[], request: IncomingMessage) => void): this; (event: "close" | "listening", cb: (this: Server) => void): this; (event: string | symbol, listener: (this: Server, ...args: any[]) => void): this; }'.

15 on(event: 'headers', cb: (this: WebSocket, headers: string[], request: http.IncomingMessage) => void): this;
~~

node_modules/websocket-stream/index.d.ts:16:5 - error TS2416: Property 'on' in type 'Server' is not assignable to the same property in base type 'Server'.
Type '{ (event: "connection", cb: (this: Server, socket: WebSocket, request: IncomingMessage) => void): this; (event: "error", cb: (this: WebSocket, error: Error) => void): this; (event: "headers", cb: (this: WebSocket, headers: string[], request: IncomingMessage) => void): this; (event: "listening", cb: (this: WebSocket) => void): this; (event: "stream", cb: (this: WebSocket, stream: WebSocketDuplex, request: IncomingMessage) => void): this; (event: string | symbol, listener: (this: WebSocket, ...args: any[]) => void): this; }' is not assignable to type '{ (event: "connection", cb: (this: Server, socket: WebSocket, request: IncomingMessage) => void): this; (event: "error", cb: (this: Server, error: Error) => void): this; (event: "headers", cb: (this: Server, headers: string[], request: IncomingMessage) => void): this; (event: "close" | "listening", cb: (this: Server) => void): this; (event: string | symbol, listener: (this: Server, ...args: any[]) => void): this; }'.

16 on(event: 'listening', cb: (this: WebSocket) => void): this;
~~

node_modules/websocket-stream/index.d.ts:17:5 - error TS2416: Property 'on' in type 'Server' is not assignable to the same property in base type 'Server'.
Type '{ (event: "connection", cb: (this: Server, socket: WebSocket, request: IncomingMessage) => void): this; (event: "error", cb: (this: WebSocket, error: Error) => void): this; (event: "headers", cb: (this: WebSocket, headers: string[], request: IncomingMessage) => void): this; (event: "listening", cb: (this: WebSocket) => void): this; (event: "stream", cb: (this: WebSocket, stream: WebSocketDuplex, request: IncomingMessage) => void): this; (event: string | symbol, listener: (this: WebSocket, ...args: any[]) => void): this; }' is not assignable to type '{ (event: "connection", cb: (this: Server, socket: WebSocket, request: IncomingMessage) => void): this; (event: "error", cb: (this: Server, error: Error) => void): this; (event: "headers", cb: (this: Server, headers: string[], request: IncomingMessage) => void): this; (event: "close" | "listening", cb: (this: Server) => void): this; (event: string | symbol, listener: (this: Server, ...args: any[]) => void): this; }'.

17 on(event: 'stream', cb: (this: WebSocket, stream: WebSocketDuplex, request: http.IncomingMessage) => void): this;
~~

Type '{ (event: "connection", cb: (this: Server, socket: WebSocket, request: IncomingMessage) => void): this; (event: "error", cb: (this: WebSocket, error: Error) => void): this; (event: "headers", cb: (this: WebSocket, headers: string[], request: IncomingMessage) => void): this; (event: "listening", cb: (this: WebSocket) => void): this; (event: "stream", cb: (this: WebSocket, stream: WebSocketDuplex, request: IncomingMessage) => void): this; (event: string | symbol, listener: (this: WebSocket, ...args: any[]) => void): this; }' is not assignable to type '{ (event: "connection", cb: (this: Server, socket: WebSocket, request: IncomingMessage) => void): this; (event: "error", cb: (this: Server, error: Error) => void): this; (event: "headers", cb: (this: Server, headers: string[], request: IncomingMessage) => void): this; (event: "close" | "listening", cb: (this: Server) => void): this; (event: string | symbol, listener: (this: Server, ...args: any[]) => void): this; }'.

18 on(event: string | symbol, listener: (this: WebSocket, ...args: any[]) => void): this;
```

The fix seems to be changing `index.d.ts` from:
```ts
on(event: 'connection', cb: (this: WebSocket.Server, socket: WebSocket, request: http.IncomingMessage) => void): this;
on(event: 'error', cb: (this: WebSocket, error: Error) => void): this;
on(event: 'headers', cb: (this: WebSocket, headers: string[], request: http.IncomingMessage) => void): this;
on(event: 'listening', cb: (this: WebSocket) => void): this;
on(event: 'stream', cb: (this: WebSocket, stream: WebSocketDuplex, request: http.IncomingMessage) => void): this;
on(event: string | symbol, listener: (this: WebSocket, ...args: any[]) => void): this;
```

to:
```ts
on(event: 'connection', cb: (this: Server, socket: WebSocket, request: http.IncomingMessage) => void): this;
on(event: 'error', cb: (this: Server, error: Error) => void): this;
on(event: 'headers', cb: (this: Server, headers: string[], request: http.IncomingMessage) => void): this;
on(event: 'listening', cb: (this: Server) => void): this;
on(event: 'stream', cb: (this: Server, stream: WebSocketDuplex, request: http.IncomingMessage) => void): this;
on(event: string | symbol, listener: (this: Server, ...args: any[]) => void): this;
```

which matches the typings for `WebSocket.Server`

Update the declarations in index.d.ts, focusing on the Server.on overloads shown in the issue. Reproduce the failure with TypeScript and @types/express-ws, then run tsc again; done means the reported TS2416 errors no longer occur and the Server callback typings match the intended Server type.

Written by the indexing model from the issue text.