Change travis badge to only show the master status

Author: ValentinH

README.md

@@ -3,7 +3,7 @@
 Status:
 [![npm version](https://img.shields.io/npm/v/angularjs-slider.svg?style=flat-square)](https://www.npmjs.com/package/angularjs-slider)
 [![npm downloads](https://img.shields.io/npm/dm/angularjs-slider.svg?style=flat-square)](http://npm-stat.com/charts.html?package=angularjs-slider&from=2015-01-01)
-[![Build Status](https://img.shields.io/travis/angular-slider/angularjs-slider.svg?style=flat-square)](https://travis-ci.org/angular-slider/angularjs-slider)
+[![Build Status](https://img.shields.io/travis/angular-slider/angularjs-slider/master.svg?style=flat-square)](https://travis-ci.org/angular-slider/angularjs-slider)
 [![codecov.io](https://img.shields.io/codecov/c/github/angular-slider/angularjs-slider.svg?style=flat-square)](https://codecov.io/github/angular-slider/angularjs-slider?branch=master)
 ![License](https://img.shields.io/badge/License-MIT-blue.svg?style=flat-square)