Update _clearfix.scss to three-line modern clearfix

Use a more modern *three line* clearfix based on Nicolas Gallagher's 2011 micro clearfix, as announced and explained by Thierry Koblentz here: http://www.css-101.org/articles/clearfix/latest-new-clearfix-so-far.php.

This is used by Inuit.css, so it's certified legit.
Remove extraneous comments

Removed clause on lack of IE7 support, given the assumption that users
are already aware Bourbon supports IE9+.

Removed credit to Nicolas Gallagher's micro-clearfix, given that the
"beat that" clearfix is based upon it and credits it in the
explanation page.
Remove extraneous comments

Remove clause on lack of IE7 support, given the assumption that users
are already aware Bourbon supports IE9+.

Remove credit to Nicolas Gallagher's micro-clearfix, given that the
"beat that" clearfix is based upon it and credits it in the
explanation page.
Merge branch 'patch-1' of https://github.com/twome/bourbon into patch-1
Update _clearfix.scss

Jesus. I can't believe I missed that.
Merge remote-tracking branch 'twome/patch-1'