It depends on how you integrate bootstrap: there's a SCSS conversion of Bootstrap that avoids the dependency on therubyracer, (it just requires sass):
https://github.com/anjlab/bootstrap-rails
Yes, I recognize that. Perhaps I didn't explain it clearly in the post. Nine of the teams used coffeescript, but only six used therubyracer. What did they use for js if not therubyracer? I'm guessing node.