Fix Size output for locales that use non-period decimal separators

[slusarz]

e.g., a locale like pt_PT parses this:

width: 0.15em;

as "0,15".

[slusarz]

The test case can be a bit misleading since, if the pt_PT locale is not installed on your system and you are using a locale that has '.' as a decimal separator, you will never see this case fail even before the patch.

[sabberworm]

Well we can’t account for any possibility. I’ve recently had someone point out to me that @keyframes support didn’t work on case-sensitive file systems because the author of the original pull request included the Keyframe class at one point instead of KeyFrame.