Typo in rx.didExitPreloadState implementation

[kirillsh]

There is a typo in implementation of didExitPreloadState computed var.
Instead of listening to didExitPreloadState method invocation it is listening to
didEnterPreloadState:

public var didExitPreloadState: ControlEvent<Void> {
    let source =  self.methodInvoked(#selector(Base.didEnterPreloadState)).map { _ in return }
    return ControlEvent(events: source)
}