[fixed] velocity
[fixed] velocity

Summary: Was being set to 0 because Rebound internally resets it if you don't pass a second argument to `setCurrentValue`.

Reviewers: O2 Material Motion, O3 Material JavaScript platform reviewers, #material_motion, markwei

Reviewed By: O2 Material Motion, #material_motion, markwei

Tags: #material_motion

Differential Revision: http://codereview.cc/D3166

material-motion/material-motion-js,material-motion/material-motion-js,material-motion/material-motion-js