Update README to include version badge

Author: mattphillips

README.md

@@ -1,9 +1,9 @@
 # Deep Object Diff
 
-[![Greenkeeper badge](https://badges.greenkeeper.io/mattphillips/deep-object-diff.svg)](https://greenkeeper.io/)
-
+[![npm version](https://badge.fury.io/js/deep-object-diff.svg)](https://badge.fury.io/js/deep-object-diff)
 [![Build Status](https://travis-ci.org/mattphillips/deep-object-diff.svg?branch=master)](https://travis-ci.org/mattphillips/deep-object-diff)
 [![Coverage Status](https://coveralls.io/repos/github/mattphillips/deep-object-diff/badge.svg?branch=master)](https://coveralls.io/github/mattphillips/deep-object-diff?branch=master)
+[![Greenkeeper badge](https://badges.greenkeeper.io/mattphillips/deep-object-diff.svg)](https://greenkeeper.io/)
 
 A small library that can deep diff two JavaScript Objects, including nested structures of arrays and objects.