Add ClojureScript extension to Clojure language in languages.coffee

ClojureScript is a compiler for Clojure that shares the same syntax as Clojure, but uses `.cljs` as its file type. I propose the "Clojure" language supports both `.clj` and `.cljs` files as both types can be used inside a Clojure application.
Merge pull request #107 from rkneufeld/patch-1

Add ClojureScript extension to Clojure language in languages.coffee