added official travis ci build status badge to readme

Author: vdemedes

Readme.md

@@ -4,7 +4,7 @@ Awesome ES6 generator-based MongoDB ODM for Node.js v0.11.x (or newer).
 Just take a look on its pretty models and beautiful API. 
 Uses [monk](https://github.com/Automattic/monk) under the hood.
 
-![Build status](https://img.shields.io/travis/vdemedes/mongorito.svg)
+[![Build Status](https://travis-ci.org/vdemedes/mongorito.svg)](https://travis-ci.org/vdemedes/mongorito)
 
 ## Features