Update columns mixin to prevent @extend being called within @media rules

[Christoph Saxe]

The column mixin previously changed to remove the arbitrary breakpoint, and is now used (almost) exclusively within @media rules. It still contains two @extend directives, however, which are not permitted within @media rules. The extends can be seen in mixins/grid/_semantic-grid.scss on line 88 and line 76.

I'd recommend removing both extend rules and inserting the css:

    float: $defaultFloat;
    margin: 0;
    min-height: 1px;

from %column-config directly before the logic block in the mixin.

[Dan Manchester]

Fixed in 2.2.4