Fix link to CONTRIBUTING.md

Author: kandalf

README.md

@@ -149,7 +149,7 @@ Please [refer to the usage documentation for more information on common pitfalls
 
 ##Contributing
 
-For contributing read [CONTRIBUTING.md](https://github.com/threefunkymonkeys/ruby-driver/blob/master/CONTRIBUTING.md)
+For contributing read [CONTRIBUTING.md](https://github.com/datastax/ruby-driver/blob/master/CONTRIBUTING.md)
 
 ## Credits