Restore gaps in links underline in iOS 8+ and Safari 8+

[antons]

#573 introduced the change. I propose to revert it, because:

1. It breaks iOS and macOS platform conventions: underlines are always drawn with “ink” style in native text views.
2. It’s a step back for web typography. Apple intentionally set the browser default to “ink” to make underlined text more readable.
3. The lack of this rule doesn’t affect other browsers, but its presence is harmful.

[jonathantneal]

@antons, thanks for this PR. I hope it gets merged! I think we should always fall forward.

Link to the draft spec: https://drafts.csswg.org/css-text-decor-4/#text-decoration-skip-ink-property
Link to Chrome status: https://www.chromestatus.com/feature/5631679087509504

[necolas]

Merged ff155ff

[antons]

Thanks! Happy to see this merged.