Use latest gradient syntax for unprefixed version

The latest linear-gradient-syntax needs other angles to work properly due to the specification changes.
Browsers that render the latest un-prefixed syntax will fail otherwise.
Compass does not support the latest syntax. Please see this bug: chriseppstein/compass#965
This is a workaround until Compass fixes this behavior.

This currently breaks the page in Chrome Canary.

Any objections?