Move NSDateFormatter to instance var. Add timestamp to dispose
Move NSDateFormatter to instance var. Add timestamp to dispose

hsoi/RxSwift,cfraz89/RxSwift,hsoi/RxSwift,KyoheiG3/RxSwift,ReactiveX/RxSwift,hsoi/RxSwift,cfraz89/RxSwift,kzaher/RxSwift,thanegill/RxSwift,thanegill/RxSwift,kzaher/RxSwift,shiratsu/RxSwift,tottakai/RxSwift,shiratsu/RxSwift,tottakai/RxSwift,tottakai/RxSwift,cfraz89/RxSwift,cfraz89/RxSwift,ReactiveX/RxSwift,kzaher/RxSwift,thanegill/RxSwift,kzaher/RxSwift,thanegill/RxSwift,shiratsu/RxSwift,KyoheiG3/RxSwift,hsoi/RxSwift,ReactiveX/RxSwift,KyoheiG3/RxSwift