Update README's KVO to match new API
Update README's KVO to match new API

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