[CLEANUP] Consistently use once space after a colon in a rule in add-ons/.

This fixes the following scss-lint warning:

"Colon after property should be followed by 1 space"

This is part of an effort to fix all scss-lint warnings in yaml.
Merge pull request #51 from braingourmets/space-after-colon

[CLEANUP] Consistently use one space after a colon in a rule in add-ons.