Added Gem Version Badge

Author: jonasjabari

README.md

@@ -1,5 +1,6 @@
 [![CircleCI](https://circleci.com/gh/basemate/matestack-ui-core/tree/master.svg?style=shield)](https://circleci.com/gh/basemate/matestack-ui-core/tree/master)
 [![Gitter](https://badges.gitter.im/basemate/community.svg)](https://gitter.im/basemate/community?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
+[![Gem Version](https://badge.fury.io/rb/matestack-ui-core.svg)](https://badge.fury.io/rb/matestack-ui-core)
 
 ![matestack logo](./logo.png)