jp_ws_fetch: passthrough kwargs to websocket_connect (#78)

allows setting things like subprotocols

pytest_jupyter/jupyter_server.py

@@ -328,7 +328,7 @@ def client_fetch(*parts, headers=None, params=None, **kwargs):
             headers.setdefault(key, value)
         # Make request.
         req = tornado.httpclient.HTTPRequest(url, headers=headers, connect_timeout=120)
-        return tornado.websocket.websocket_connect(req)
+        return tornado.websocket.websocket_connect(req, **kwargs)
 
     return client_fetch