Add test for StaggeredMotion
Add test for StaggeredMotion

Also includes the test for 7a9e986a377a112057a68831f895dcf485916598

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