add gem version batch to README.MD

Thanks for merging #28. This is just a shortcut to find the latest gem version faster.

Author: mtmail

README.md

@@ -4,7 +4,7 @@ A Ruby toolkit for the [Drip](https://www.getdrip.com/) API.
 
 [![Build Status](https://travis-ci.org/DripEmail/drip-ruby.svg?branch=master)](https://travis-ci.org/DripEmail/drip-ruby)
 [![Code Climate](https://codeclimate.com/github/DripEmail/drip-ruby/badges/gpa.svg)](https://codeclimate.com/github/DripEmail/drip-ruby)
-
+[![Gem Version](https://badge.fury.io/rb/drip-ruby.svg)](https://badge.fury.io/rb/drip-ruby)
 
 
 ## Installation