No Await Expression for Websocket Closing

[wes8ty]

Was testing this library out and the following line self._websocket.close(code) needs an await

async def close(self, code: int = 1000):
    if self._websocket is not None:
        # Case opened, we have something to close.
        self._websocket.close(code)

[orweis]

Want to open a PR? :)