Use yarn instead of NPM

Author: SeyZ

README.md

@@ -4,7 +4,9 @@
   <img src="https://github.com/SeyZ/jsonapi-serializer/blob/master/logo.jpg?raw=true" alt="JSONAPI Serializer Logo">
 </p>
 
-[![Build Status](https://travis-ci.org/SeyZ/jsonapi-serializer.svg?branch=master)](https://travis-ci.org/SeyZ/jsonapi-serializer) [![npm version](https://img.shields.io/npm/v/jsonapi-serializer.svg)](https://www.npmjs.com/package/jsonapi-serializer)
+[![Build Status](https://travis-ci.org/SeyZ/jsonapi-serializer.svg?branch=master)](https://travis-ci.org/SeyZ/jsonapi-serializer)
+[![npm version](https://img.shields.io/npm/v/jsonapi-serializer.svg)](https://yarnpkg.com/en/package/jsonapi-serializer)
+[![download](https://img.shields.io/npm/dm/jsonapi-serializer.svg)](https://yarnpkg.com/en/package/jsonapi-serializer)
 
 A Node.js framework agnostic library for (de)serializing your data to [JSON
 API](http://jsonapi.org) (1.0 compliant).