Fix bug where cancelling operations caused the queue to stop
Fix bug where cancelling operations caused the queue to stop

BoxAPIOperation did not properly set the KVO properties for NSOperations when
cancelling operations

flatworld/box-ios-sdk-v2,Taptera/deprecated-box-ios-sdk,DocuSignDev/box-ios-sdk-v2,CleanShavenApps/box-ios-sdk-v2,Taptera/deprecated-box-ios-sdk,doo/box-ios-sdk-v2,doo/box-ios-sdk-v2,clariussystems/box-ios-sdk-v2,mirego/box-ios-sdk-v2,mirego/box-ios-sdk-v2,Taptera/deprecated-box-ios-sdk,CleanShavenApps/box-ios-sdk-v2,clariussystems/box-ios-sdk-v2,CleanShavenApps/box-ios-sdk-v2,flatworld/box-ios-sdk-v2,doo/box-ios-sdk-v2,DocuSignDev/box-ios-sdk-v2,DocuSignDev/box-ios-sdk-v2,doo/box-ios-sdk-v2,flatworld/box-ios-sdk-v2