Fix typo with AsyncClient.connect example (#1403)

Author: ZeroIntensity

src/socketio/async_client.py

@@ -116,7 +116,7 @@ async def connect(self, url, headers={}, auth=None, transports=None,
         Example usage::
 
             sio = socketio.AsyncClient()
-            sio.connect('http://localhost:5000')
+            await sio.connect('http://localhost:5000')
         """
         if self.connected:
             raise exceptions.ConnectionError('Already connected')