Removed strong reference to RACDisposable.
Removed strong reference to RACDisposable.

jspahrsummers/FunctionalReactivePixels,hbucius/FunctionalReactivePixels,SilenceZhou/FunctionalReactivePixels,fxd/FunctionalReactivePixels,sandyway/FunctionalReactivePixels,ManagerOrganization/FunctionalReactivePixels,LiuShulong/FunctionalReactivePixels,RiuHDuo/FunctionalReactivePixels,ashfurrow/FunctionalReactivePixels