Calendar: Fix .date-day gradient background

Was using incorrect syntax for the Compass mixin as pointed out in
gh-1158
Removing 'top' direction for linear gradient

This is the default value and will avoid the issue where Compass
currenty doesn't convert the non-vendor property to the official CSS3
syntax
Merge pull request #1297 from nschonni/fix-date-day-gradient

Util-screen and Slider: Fix some CSS3 gradient format issues