Fixed invalid badge (code coverage).

Author: pomek

README.md

@@ -4,7 +4,8 @@ CKEditor 5 highlight feature
 [![Join the chat at https://gitter.im/ckeditor/ckeditor5](https://badges.gitter.im/ckeditor/ckeditor5.svg)](https://gitter.im/ckeditor/ckeditor5?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 [![npm version](https://badge.fury.io/js/%40ckeditor%2Fckeditor5-highlight.svg)](https://www.npmjs.com/package/@ckeditor/ckeditor5-highlight)
 [![Build Status](https://travis-ci.org/ckeditor/ckeditor5-highlight.svg?branch=master)](https://travis-ci.org/ckeditor/ckeditor5-highlight)
-[![Test Coverage](https://codeclimate.com/github/ckeditor/ckeditor5-highlight/badges/coverage.svg)](https://codeclimate.com/github/ckeditor/ckeditor5-highlight/coverage)
+[![Coverage Status](https://coveralls.io/repos/github/ckeditor/ckeditor5-highlight/badge.svg?branch=master)](https://coveralls.io/github/ckeditor/ckeditor5-highlight?branch=master)
+<br>
 [![Dependency Status](https://david-dm.org/ckeditor/ckeditor5-highlight/status.svg)](https://david-dm.org/ckeditor/ckeditor5-highlight)
 [![devDependency Status](https://david-dm.org/ckeditor/ckeditor5-highlight/dev-status.svg)](https://david-dm.org/ckeditor/ckeditor5-highlight?type=dev)