Set default icon branch to master

Author: Marco Paolini

README.rst

@@ -4,7 +4,7 @@ Pushpull
 A websocket to rabbitmq gateway
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-.. image:: https://travis-ci.org/elastic-coders/pushpull.svg?branch=develop
+.. image:: https://travis-ci.org/elastic-coders/pushpull.svg?branch=master
     :target: https://travis-ci.org/elastic-coders/pushpull
 
 **BETA**