update coveralls.io

Author: troolee

README.md

@@ -2,7 +2,7 @@ gridstack.js
 ============
 
 [![Build Status](https://travis-ci.org/gridstack/gridstack.js.svg?branch=develop)](https://travis-ci.org/gridstack/gridstack.js)
-[![Coverage Status](https://coveralls.io/repos/github/troolee/gridstack.js/badge.svg?branch=master)](https://coveralls.io/github/troolee/gridstack.js?branch=master)
+[![Coverage Status](https://coveralls.io/repos/github/gridstack/gridstack.js/badge.svg?branch=develop)](https://coveralls.io/github/gridstack/gridstack.js?branch=develop)
 [![Dependency Status](https://david-dm.org/troolee/gridstack.js.svg)](https://david-dm.org/troolee/gridstack.js)
 [![devDependency Status](https://david-dm.org/troolee/gridstack.js/dev-status.svg)](https://david-dm.org/troolee/gridstack.js#info=devDependencies)