Bring back build status

README.md

@@ -1,4 +1,4 @@
-# React Native [![npm version](https://badge.fury.io/js/react-native.svg)](http://badge.fury.io/js/react-native)
+# React Native [![Build Status](https://travis-ci.org/facebook/react-native.svg?branch=master)](https://travis-ci.org/facebook/react-native)  [![npm version](https://badge.fury.io/js/react-native.svg)](http://badge.fury.io/js/react-native)
 
 React Native enables you to build world-class application experiences on native platforms using a consistent developer experience based on JavaScript and [React](http://facebook.github.io/react). The focus of React Native is on developer efficiency across all the platforms you care about - learn once, write anywhere. Facebook uses React Native in multiple production apps and will continue investing in React Native.