Prevent Websocket send from hanging if connection fails.

[vincev]

I have just found out that the following code hangs if no server is running on port 9321:

let ws = WebSocket::open("ws://localhost:9321").unwrap();
let (mut sender, mut receiver) = ws.split();
let _ = sender.send(Message::Text("test".into())).await;

this is because if the server is not running the open_callback is not called and the waker is not waked causing poll_ready to always return Pending.

This PR adds a wake() call on the error_callback so that poll_ready will move to Ready also if an error occurs.

[vincev]

Checked the lint errors they are from another crate not affected by this PR, please let me know if you would like them fixed with this PR.

[futursolo]

LGTM.

I have created #287 to fix clippy.

[ranile]

Released in gloo-net 0.2.6 🎉