Tighten legacy color conversion

The existing regex was only separating on comma,
but `var()` statements (which can be used as values)
can also include a comma (after which follows a
default value)

This seemed to be the case in one instance in Bootstrap,
causing it to be minified incorrectly.

This replacement is more strict, and will only
convert colors made up of their literal values,
ignoring any that include `var()`s in there.

Fixes #422

make format

Fix PHP 5.5 tests

Merge branch 'Visualq-master'

Fix bug #395 Calc function missing on background-position property

Add convenience var for testing only certain paths

Merge branch 'rowhel95-rowhel95-patch-1'

Make test suite pass for all PHP versions

Don't install libzip for more recent php versions

Add test for #349