invalid type definition for RetryInterceptor

there seems to be an error in the type definition of RetryInterceptor

aurelia-fetch-client 1.8.0
typescript 3.2.4

https://github.com/aurelia/fetch-client/blob/fa53ec779f2e0937129010e952c57568842bd46b/dist/aurelia-fetch-client.d.ts#L310`

```
error TS2416: Property 'response' in type 'RetryInterceptor' is not assignable to the same property in base type 'Interceptor'.
Type '(response: Response, request: Request) => Response' is not assignable to type '(response: Response, request?: Request | undefined) => Response | Promise'.
Types of parameters 'request' and 'request' are incompatible.
Type 'Request | undefined' is not assignable to type 'Request'.
Type 'undefined' is not assignable to type 'Request'.
```

Open dist/aurelia-fetch-client.d.ts at line 310 and inspect the RetryInterceptor response definition alongside the Interceptor signature shown in the TypeScript error. Reproduce the reported TypeScript 3.2.4 compilation error, then verify that the corrected declaration compiles without TS2416.

Written by the indexing model from the issue text.