WebSocket connect error is not forwarded

[mkosieradzki]

Opening as requested in #41

Currently due to lack of WebException support in netstandard13 in case of connect error, a generic 400 error is returned instead of forwarding original response.

In full .NET Framework following code could be used to extract the original response

var res = (ex.InnerException as WebException)?.Response;

[aspnet-hello]

This issue was moved to aspnet/Home#2494