removed outdated vendor prefixes

-o- has been removed before switching to webkit/blink.
-moz- removed since Firefox 15 (few years ago?), except ::-moz-selection as of FF32
-webkit- remains; Safari 6.1 & Android 4.3
`transform` added; in use.
http://caniuse.com/#search=transition
http://caniuse.com/#search=transform

`#contributors {` was too long to be readable.