chore(readme): Update badges

Author: rpl

README.md

@@ -3,10 +3,11 @@
 This is a command line tool to help build, run, and test
 [WebExtensions](https://wiki.mozilla.org/WebExtensions).
 
-[![Build Status](https://travis-ci.org/mozilla/web-ext.svg?branch=master)](https://travis-ci.org/mozilla/web-ext)
-[![Coverage Status](https://coveralls.io/repos/github/mozilla/web-ext/badge.svg?branch=master)](https://coveralls.io/github/mozilla/web-ext?branch=master)
+[![CircleCI](https://circleci.com/gh/mozilla/web-ext.svg?style=svg)](https://circleci.com/gh/mozilla/web-ext)
+[![codecov](https://codecov.io/gh/mozilla/web-ext/branch/master/graph/badge.svg)](https://codecov.io/gh/mozilla/web-ext)
 [![Dependency Status](https://david-dm.org/mozilla/web-ext.svg)](https://david-dm.org/mozilla/web-ext)
 [![devDependency Status](https://david-dm.org/mozilla/web-ext/dev-status.svg)](https://david-dm.org/mozilla/web-ext#info=devDependencies)
+[![npm version](https://badge.fury.io/js/web-ext.svg)](https://badge.fury.io/js/web-ext)
 
 Ultimately, it aims to support browser extensions in a standard, portable,
 cross-platform way. Initially, it will provide a streamlined experience for developing