Use string key for TransitionStyle/TransitionPlainStyle in tests
Use string key for TransitionStyle/TransitionPlainStyle in tests

See 647a1db74e7a77daf3341e088a4790d461536067

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