Travis CI: use flat badge

Signed-off-by: Vincent Giersch <vincent.giersch@ovh.net>

Author: gierschv

README.md

@@ -3,7 +3,7 @@
 The easiest way to use the [OVH.com](http://ovh.com) APIs in your [node.js](http://nodejs.org/) applications.
 
 [![NPM Version](https://img.shields.io/npm/v/ovh.svg?style=flat)](https://www.npmjs.org/package/express)
-[![Build Status](https://secure.travis-ci.org/ovh/node-ovh.png?style=flat)](http://travis-ci.org/ovh/node-ovh)
+[![Build Status](https://img.shields.io/travis/ovh/node-ovh.svg?style=flat)](http://travis-ci.org/ovh/node-ovh)
 [![Coverage Status](https://img.shields.io/coveralls/ovh/node-ovh.svg?style=flat)](https://coveralls.io/r/ovh/node-ovh?branch=master)
 
 ```js