Keep the coverage badge

README.md

@@ -1,6 +1,7 @@
 [![npm](https://img.shields.io/npm/v/microstates.svg)](https://www.npmjs.com/package/microstates)
 [![bundle size (minified + gzip)](https://badgen.net/bundlephobia/minzip/microstates)](https://bundlephobia.com/result?p=microstates)
 [![Build Status](https://travis-ci.org/microstates/microstates.js.svg?branch=master)](https://travis-ci.org/microstates/microstates.js)
+[![Coverage Status](https://coveralls.io/repos/github/microstates/microstates.js/badge.svg?branch=master)](https://coveralls.io/github/microstates/microstates.js?branch=master)
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
 [![Gitter](https://badges.gitter.im/microstates/microstates.js.svg)](https://gitter.im/microstates/microstates.js?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
 [![Created by The Frontside](https://img.shields.io/badge/created%20by-frontside.io-blue.svg)](https://frontside.io)