Pin version of uhashring to support py27. (#142)

Author: umaannamalai

tox.ini

@@ -161,6 +161,7 @@ deps =
     cross_agent: requests
     datastore_asyncpg: asyncpg
     datastore_bmemcached-memcached030: python-binary-memcached<0.31
+    datastore_bmemcached-memcached030: uhashring<2.0
     datastore_elasticsearch: requests
     datastore_elasticsearch-elasticsearch00: elasticsearch<1.0
     datastore_elasticsearch-elasticsearch01: elasticsearch<2.0