shouldComponentUpdate should return a boolean value instead of undefined
shouldComponentUpdate should return a boolean value instead of undefined

Fixes the following warning:
ReactCompositeComponent.shouldComponentUpdate(): Returned undefined instead of a boolean value. Make sure to return true or false.
jed/react-swipe,heardy/react-swipe,BunHouth/react-swipe,tilfab/react-swipe,voronianski/react-swipe,tchret/react-swipe,pogoseat/react-swipe,jed/react-swipe,dazld/react-swipe,maoziliang/react-swipe,tilfab/react-swipe,BunHouth/react-swipe,maoziliang/react-swipe,matthewmueller/react-swipe,Seedstars/react-swipe,pogoseat/react-swipe,tchret/react-swipe,dazld/react-swipe,Seedstars/react-swipe,matthewmueller/react-swipe,heardy/react-swipe