add coverage badeg

[skip ci]

Author: sabakugaara

README.md

@@ -1,5 +1,5 @@
 # 又拍云 PHP SDK
-[![Build Status](https://scrutinizer-ci.com/g/upyun/php-sdk/badges/build.png?b=master)](https://scrutinizer-ci.com/g/upyun/php-sdk/build-status/master) [![Scrutinizer Code Quality](https://scrutinizer-ci.com/g/upyun/php-sdk/badges/quality-score.png?b=master)](https://scrutinizer-ci.com/g/upyun/php-sdk/?branch=master)
+[![Build Status](https://scrutinizer-ci.com/g/upyun/php-sdk/badges/build.png?b=master)](https://scrutinizer-ci.com/g/upyun/php-sdk/build-status/master) [![Scrutinizer Code Quality](https://scrutinizer-ci.com/g/upyun/php-sdk/badges/quality-score.png?b=master)](https://scrutinizer-ci.com/g/upyun/php-sdk/?branch=master) [![Code Coverage](https://scrutinizer-ci.com/g/upyun/php-sdk/badges/coverage.png?b=master)](https://scrutinizer-ci.com/g/upyun/php-sdk/?branch=master) 
 
 又拍云存储PHP SDK，基于[又拍云存储 HTTP API 接口](http://docs.upyun.com/api/) 开发。SDK 包含了文件上传下载刷新等基本操作，以及图片、视频云处理等功能。