A fix for UIImage category

[croath]

Fixes according to #11

[liangdrime]

I'm glad to that you solved this issue used my code.
And, is it a mistake in category of UIImageView offset.y = finalSize.height = size.height when move vertical of the layer?
I think it should be offset.y = finalSize.height - size.height,would you please check out it?

[croath]

@Roylee-ML It got fixed. Thanks so much for your help!