Update README.md

Author: troolee

README.md

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 gridstack.js
 ============
 
+[![Build Status](https://travis-ci.org/troolee/gridstack.js.svg?branch=master)](https://travis-ci.org/troolee/gridstack.js)
+
 gridstack.js is a jQuery plugin for widget layout. This is drag-and-drop multi-column grid. It allows you to build
 draggable responsive bootstrap v3 friendly layouts. It also works great with [knockout.js](http://knockoutjs.com), [angular.js](https://angularjs.org) and touch devices.