Add some tests for stripStyle()
Add some tests for stripStyle()

While fixing #180, I noticed that stripStyle() was untested, so I
decided to add a couple of basic tests here.

chenglou/react-motion,keyanzhang/react-motion,dieface/react-motion,chenglou/react-motion,BenoitZugmeyer/preact-motion,bishopZ/react-motion,dieface/react-motion,threepointone/react-motion,BenoitZugmeyer/preact-motion,bishopZ/react-motion,threepointone/react-motion,keyanzhang/react-motion