Small PEP8 corrections

publish_subscribe.py

@@ -1,10 +1,10 @@
 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
 
-'''
+"""
 Reference: http://www.slideshare.net/ishraqabd/publish-subscribe-model-overview-13368808
 Author: https://github.com/HanWenfang
-'''
+"""
 
 
 class Provider: