Broken Stream Client Connection

I was trying out the SDK and I found an issue while testing the **crypto stream** and the **data stream** examples. The issue may be with the actual `stream.CryptoClient` / `stream.StocksClient` and how it tries to connect.

When I called the `Connect(...)` method I got the following error:

```
datav2stream: irrecoverable error: websocket dial: failed to WebSocket dial: expected handshake response status code 101 but got 404
```

The key to fixing it was in the log line immediately before:

```
datav2stream: connecting to wss://paper-api.alpaca.markets/stream/us, attempt 1/20 ...
```

The `/us` shouldn't be there.

I was able to get around this error by creating the clients with `marketdata.Feed("")` for the first param. This way I got a log:

```
datav2stream: established connection
```