In order to upgrade this package, it's currently easiest to follow those steps:

Checkout https://github.com/twbs/bootstrap-sass and enter the directory.
Check the hash of the version of bootstrap-scss that you want to build in
https://github.com/twbs/bootstrap repository.
Run "rake -v convert[the-hash-of-the-commit]".
Copy all files from assets/javascripts to data/js.
Copy all files from assets/fonts to data/fonts.
Copy all files from assets/stylesheets to data/scss.
Bump the version in __init__.py and run xstatic-release.
Commit the new files.