WebsocketHandler.get is async

As of Tornado v6.0.2 some methods were converted to be async/await capable. See commit:

tornadoweb/tornado@e69becb

Author: rmorshea

jupyter_server_proxy/websocket.py

@@ -85,8 +85,7 @@ def undisallow(*args2, **kwargs2):
     async def get(self, *args, **kwargs):
         if self.request.headers.get("Upgrade", "").lower() != 'websocket':
             return await self.http_get(*args, **kwargs)
-        # super get is not async
-        super().get(*args, **kwargs)
+        await super().get(*args, **kwargs)