Add coveralls badge

README.md

@@ -1,6 +1,7 @@
 jieba-php
 ========
 [![Build Status](https://travis-ci.org/fukuball/jieba-php.svg?branch=master)](https://travis-ci.org/fukuball/jieba-php)
+[![Coverage Status](https://coveralls.io/repos/fukuball/jieba-php/badge.svg?branch=master)](https://coveralls.io/r/fukuball/jieba-php?branch=master)
 [![Latest Stable Version](https://poser.pugx.org/fukuball/jieba-php/v/stable.png)](https://packagist.org/packages/fukuball/jieba-php)
 
 "結巴"中文分詞：做最好的 PHP 中文分詞、中文斷詞組件，目前翻譯版本為 jieba-0.16 版本，未來再慢慢往上升級，效能也需要再改善，請有興趣的開發者一起加入開發！若想使用 Python 版本請前往 [fxsjy/jieba](https://github.com/fxsjy/jieba)