Add Travis badge

Author: jakezatecky

README.md

@@ -1,6 +1,7 @@
 # react-checkbox-tree
 
 [![npm](https://img.shields.io/npm/v/react-checkbox-tree.svg?style=flat-square)](https://www.npmjs.com/package/react-checkbox-tree)
+[![Build Status](https://img.shields.io/travis/jakezatecky/react-checkbox-tree/master.svg?style=flat-square)](https://travis-ci.org/jakezatecky/react-checkbox-tree)
 [![Dependency Status](https://img.shields.io/david/jakezatecky/react-checkbox-tree.svg?style=flat-square)](https://david-dm.org/jakezatecky/react-checkbox-tree)
 [![devDependency Status](https://david-dm.org/jakezatecky/react-checkbox-tree/dev-status.svg?style=flat-square)](https://david-dm.org/jakezatecky/react-checkbox-tree#info=devDependencies)
 [![GitHub license](https://img.shields.io/badge/license-MIT-blue.svg?style=flat-square)](https://raw.githubusercontent.com/jakezatecky/react-checkbox-tree/master/LICENSE.txt)