does not invoke not existing methods

[madox2]

As the addListener and removeListener methods are not part of Animated interface it should be called defensively.

Specifically, I faced problem when _parent property of AnimatedInterpolation was instance of AnimatedModulo (which does not implement removeListener method). On component unmount it called __detach method which afterwards throwed an uncaught error.

[lelandrichardson]

I believe #49 should fix this, though it may not be a bad idea to add this and be defensive anyway