a bit more sassy

removed redundant clearfix class from demo, because it is already part of the rrssb css file.

condense clear fix class into nested Sass selector.

@extend out border-box as it was used in multiple selectors, rearrange so unprefixed version is last.
Merge pull request #16 from scottaohara/small_edits

a bit more sassy
generated files update after pull request