fixed path for bootstrap-sass import

the first commit is only for twbs/bootstrap-sass `<=3.1.x` !!!
since `3.2.0` it is without `vendor/` see 1st point here https://github.com/twbs/bootstrap-sass/blob/v3.2.0/CHANGELOG.md

the second commit is to get it work with `>=3.2`

so please merge the first commit to your version `3.0.0-betaX` and the second commit would be for the new twbs version 3.2+ (should be also a new version/branch in your repo).
unfortunately i don't know how to split the two commits in two branches (like `patch-1` and `patch-2`)