Add badge for latest version to README.

README.markdown

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-# pusher-fake [![Build Status](https://img.shields.io/travis/tristandunn/pusher-fake/master.svg)](https://travis-ci.org/tristandunn/pusher-fake) [![Dependency Status](http://img.shields.io/gemnasium/tristandunn/pusher-fake.svg)](https://gemnasium.com/tristandunn/pusher-fake) [![Code Climate](http://img.shields.io/codeclimate/github/tristandunn/pusher-fake.svg)](https://codeclimate.com/github/tristandunn/pusher-fake) [![Coverage Status](http://img.shields.io/coveralls/tristandunn/pusher-fake.svg)](https://coveralls.io/r/tristandunn/pusher-fake?branch=master)
+# pusher-fake [![Latest Version](https://img.shields.io/gem/v/pusher-fake.svg)](https://rubygems.org/gems/pusher-fake) [![Build Status](https://img.shields.io/travis/tristandunn/pusher-fake/master.svg)](https://travis-ci.org/tristandunn/pusher-fake) [![Dependency Status](http://img.shields.io/gemnasium/tristandunn/pusher-fake.svg)](https://gemnasium.com/tristandunn/pusher-fake) [![Code Climate](http://img.shields.io/codeclimate/github/tristandunn/pusher-fake.svg)](https://codeclimate.com/github/tristandunn/pusher-fake) [![Coverage Status](http://img.shields.io/coveralls/tristandunn/pusher-fake.svg)](https://coveralls.io/r/tristandunn/pusher-fake?branch=master)
 
 A fake [Pusher](https://pusher.com) server for development and testing.