use SVG badges

SVG badges look beautiful on retina displays.

README.md

@@ -1,6 +1,6 @@
 <p align="center"><a href="http://vuejs.org" target="_blank"><img width="100"src="http://vuejs.org/images/logo.png"></a></p>
 
-# Vue.js [![Build Status](https://travis-ci.org/yyx990803/vue.png?branch=master)](https://travis-ci.org/yyx990803/vue) [![Selenium Test Status](https://saucelabs.com/buildstatus/vuejs)](https://saucelabs.com/u/vuejs) [![Coverage Status](https://coveralls.io/repos/yyx990803/vue/badge.png)](https://coveralls.io/r/yyx990803/vue)
+# Vue.js [![Build Status](https://travis-ci.org/yyx990803/vue.svg?branch=master)](https://travis-ci.org/yyx990803/vue) [![Selenium Test Status](https://saucelabs.com/buildstatus/vuejs)](https://saucelabs.com/u/vuejs) [![Coverage Status](https://img.shields.io/coveralls/yyx990803/vue.svg)](https://coveralls.io/r/yyx990803/vue?branch=master)
 
 > MVVM made simple.