Add Gitter badge

Author: gitter-badger

README.md

@@ -1,5 +1,7 @@
 #Scala Exercises
 
+[![Join the chat at https://gitter.im/47deg/scala-exercises](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/47deg/scala-exercises?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
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 ##How it works