v4 - Collapse JavaScript - not removing a temporary style.

Created by: IceReaper

Hello,

when closing a collapse element, this line gets triggered: this._element.style[dimension] = 0 causing the correct animation but which is not overwritten by this._element.style[dimension] = '' when the transition is completed.

After closing a collapse, there is a leftover height style, which might break layout and has to be removed when close transition is finished.

Should be added around line 232.