Update badge

Author: kangkyu

README.md

@@ -6,7 +6,7 @@ Yt::Annotations is a Ruby library to fetch annotations, cards and end screens of
 The **source code** is available on [GitHub](https://github.com/fullscreen/yt-annotations) and the **documentation** on [RubyDoc](http://www.rubydoc.info/github/fullscreen/yt-annotations/Yt/Annotations).
 
 [![Build Status](http://img.shields.io/travis/Fullscreen/yt-annotations/master.svg)](https://travis-ci.org/Fullscreen/yt-annotations)
-[![Coverage Status](http://img.shields.io/coveralls/Fullscreen/yt-annotations/master.svg)](https://coveralls.io/r/Fullscreen/yt-annotations)
+[![Coverage Status](https://coveralls.io/repos/github/Fullscreen/yt-annotations/badge.svg?branch=master)](https://coveralls.io/github/Fullscreen/yt-annotations?branch=master)
 [![Dependency Status](http://img.shields.io/gemnasium/Fullscreen/yt-annotations.svg)](https://gemnasium.com/Fullscreen/yt-annotations)
 [![Code Climate](http://img.shields.io/codeclimate/github/Fullscreen/yt-annotations.svg)](https://codeclimate.com/github/Fullscreen/yt-annotations)
 [![Online docs](http://img.shields.io/badge/docs-✓-green.svg)](http://www.rubydoc.info/gems/yt-annotations/Yt/Annotations)