Bootstrap is LESS. There's a huge repo[1] for a SCSS version of Bootstrap: this repo seems to be trying to release it earlier than Thomas McDonald's version. That being said, there is a branch[2] on that repo that (at time of writing) was updated three hours ago.
[1]: https://github.com/thomas-mcdonald/bootstrap-sass
[2]: https://github.com/thomas-mcdonald/bootstrap-sass/tree/3