add badges of build, release and coverage

Author: 钟楚君

.travis.yml

@@ -18,3 +18,5 @@ deploy:
   on:
     tags: true
     repo: qiniu/js-sdk
+after_success:
+  - bash <(curl -s https://codecov.io/bash)    

README.md

@@ -1,5 +1,10 @@
 # Qiniu-JavaScript-SDK
 
+[![Build Status](https://travis-ci.org/qiniu/x.svg?branch=master)](https://travis-ci.org/qiniu/js-sdk)
+[![GitHub release](https://img.shields.io/github/v/tag/qiniu/js-sdk.svg?label=release)](https://github.com/qiniu/js-sdk/releases)
+[![Coverage Status](https://codecov.io/gh/qiniu/js-sdk/branch/master/graph/badge.svg)](https://codecov.io/gh/qiniu/js-sdk)
+
+
 基于七牛 API 开发的前端 JavaScript SDK
 
 ### 当前版本为 3.x，旧版本文档：[2.x](https://github.com/qiniu/js-sdk/tree/2.x)、[1.x](https://github.com/qiniu/js-sdk/tree/1.x)