Replace "is not" against empty string with "!="

Silences warning (or perhaps legit error, now)

Author: srh

rethinkdb/asyncio_net/net_asyncio.py

@@ -227,7 +227,7 @@ def connect(self, timeout):
                         break
                     # This may happen in the `V1_0` protocol where we send two requests as
                     # an optimization, then need to read each separately
-                    if request is not "":
+                    if request != "":
                         self._streamwriter.write(request)
 
                     response = yield from asyncio.wait_for(