update cdn

Author: troolee

README.md

@@ -82,8 +82,8 @@ Note: You can still use [underscore.js](http://underscorejs.org) (>= 1.7.0) inst
 * Using CDN:
 
 ```html
-<link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/gridstack.js/0.2.5/gridstack.min.css" />
-<script type="text/javascript" src='//cdnjs.cloudflare.com/ajax/libs/gridstack.js/0.2.5/gridstack.min.js'></script>
+<link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/gridstack.js/0.2.6/gridstack.min.css" />
+<script type="text/javascript" src='//cdnjs.cloudflare.com/ajax/libs/gridstack.js/0.2.6/gridstack.min.js'></script>
 ```
 
 * Using bower: