Issues with LESS in old bootstrap gem

[garside]

Heya, dunno whose running the show for this, but we hit a weird error because twitter-bootstrap had less included, which seemed not to be relevant to this gem at all.

I went and created #140 to use bootstrap-sass instead which seemed more in line with the other code we had here.

Seems to be passing on travis, so not sure what the next steps for this are, but seeing as how it's a drop in gem replacement, I'm not sure if there's anything else you'd need to push this across the finish line.