Fix ZeroUnit regex for colors and decimals

The `ZeroUnit` linter would incorrectly report a lint for values like
`#0af` or `4.0em`.

This was solved by adding a negative lookbehind for the `#` or `.`
characters.

Change-Id: Iab90d77155fb7ccc666fccd9524f18be14cb23b7
Reviewed-on: http://gerrit.causes.com/37219
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>