Fix bouncing scroll-down arrow bug in webkit

Webkit transform currently requires a vendor prefix. Without it, the arrow bounces and rotate to the original un-rotated state. See https://www.dropbox.com/s/46sjiihtjya42s8/wk-rotate.mov
Merge pull request #129 from Douten/patch-1

Fix bouncing scroll-down arrow bug in webkit
Merge branch 'master' into casper-custom