pyyaml update

requirements.txt

@@ -6,9 +6,9 @@ python-dateutil==2.5.3
 python-engineio==0.9.2
 python-mimeparse==1.5.2
 python-socketio==1.4.4
-PyYAML==3.11
+PyYAML==4.2b1
 requests==2.20.0
 Werkzeug==0.11.10
 httplib2==0.9.2
 flask-classy==0.6.10
-GitPython==2.1.3
+GitPython==2.1.3