chore(docs): add gzip shield

Author: Vince Speelman

README.md

@@ -2,6 +2,7 @@
 
 [![Travis](https://img.shields.io/travis/VinSpee/async-redux-actions.svg?style=flat-square)](https://travis-ci.org/VinSpee/async-redux-actions)
 [![Coverage Status](https://coveralls.io/repos/github/VinSpee/async-redux-actions/badge.svg?branch=master&style=flat-square)](https://coveralls.io/github/VinSpee/async-redux-actions?branch=master)
+[![npm bundle size (minified + gzip)](https://img.shields.io/bundlephobia/minzip/async-redux-actions.svg?style=flat-square)](https://www.npmjs.com/package/async-redux-actions)
 [![Tested with Jest](https://img.shields.io/badge/tested_with-jest-99424f.svg?longCache=true&style=flat-square)](https://github.com/facebook/jest)
 [![semantic-release](https://img.shields.io/badge/%20%20%F0%9F%93%A6%F0%9F%9A%80-semantic--release-e10079.svg?longCache=true&style=flat-square)](https://github.com/semantic-release/semantic-release)
 [![Commitizen friendly](https://img.shields.io/badge/commitizen-friendly-brightgreen.svg?longCache=true&style=flat-square)](http://commitizen.github.io/cz-cli/)