Adds gem badge to README

Author: arempe93

README.md

@@ -2,6 +2,7 @@ Bunny Mock
 ==========
 
 [![Build Status](https://travis-ci.org/arempe93/bunny-mock.svg?branch=master)](https://travis-ci.org/arempe93/bunny-mock)
+[![Gem Version](https://badge.fury.io/rb/bunny-mock.svg)](https://rubygems.org/gems/bunny-mock)
 
 A mock client for RabbitMQ, modeled after the popular [Bunny client](https://github.com/ruby-amqp/bunny). It currently supports basic usage of Bunny for managing exchanges and queues, with the goal of being able to handle and test all Bunny use cases.