Fix flake8 error

Author: ttt733

alpaca_trade_api/stream2.py

@@ -31,7 +31,7 @@ async def _connect(self):
             r = r.decode('utf-8')
         msg = json.loads(r)
 
-        if not 'data' in msg or msg['data']['status'] != 'authorized':
+        if 'data' not in msg or msg['data']['status'] != 'authorized':
             raise ValueError(
                 ("Invalid Alpaca API credentials, Failed to authenticate: {}"
                     .format(msg))