update six and PyYAML (#952)

Author: wallacbe

setup.py

@@ -133,11 +133,11 @@ def run(self):
     'mutablerecords>=0.4.1,<2.0',
     'oauth2client>=1.5.2,<2.0',
     'protobuf>=3.6.0,<4.0',
-    'PyYAML>=3.13,<4.0',
+    'PyYAML>=3.13',
     'pyOpenSSL>=17.1.0,<18.0',
     'sockjs-tornado>=1.0.3,<2.0',
     'tornado>=4.3,<5.0',
-    'six>=1.12.0',
+    'six>=1.13.0',
 ]