Return unmodified source immediately if no generator functions detected.
Return unmodified source immediately if no generator functions detected.

Closes #13.

facebook/regenerator,RReverser/js-goto-transpiler,jlongster/unwinder,liviuignat/regenerator,sebmck/regenerator,Jericho25/regenerator,facebook/regenerator,rafaelstz/regenerator,sebmck/regenerator,jlongster/transmogrifier,jlongster/unwinder,kittens/regenerator,jlongster/transmogrifier,rwaldron/regenerator,facebook/regenerator,liviuignat/regenerator,juliocanares/regenerator,kittens/regenerator,rafaelstz/regenerator,RReverser/js-goto-transpiler,Jericho25/regenerator,juliocanares/regenerator,jlongster/unwinder