Fix associated object references in UIViewController+Spec.
Fix associated object references in UIViewController+Spec.

joemasilotti/PivotalCoreKit,idoru/PivotalCoreKit,jfuchs/PivotalCoreKit,pivotaltracker/PivotalCoreKit,mjstallard/PivotalCoreKit,gudatcomputers/PivotalCoreKit,briancroom/PivotalCoreKit,jfuchs/PivotalCoreKit,joemasilotti/PivotalCoreKit,idoru/PivotalCoreKit,pivotal/PivotalCoreKit,gudatcomputers/PivotalCoreKit