KeyboardObserver 0.4.0. Fix curve property.

KeyboardObserver is a swift library which frees you from keyboard related complicated notification handling.

KeyboardObserver 0.4.0 is released now. In this release, I fixed the event.curve property.

It was UIAnimationOptions, but correctly it is UIAnimationCurve. So changed it as its correct type. At the same time, I added new options property which acts as older curve, UIAnimationOptions.