Revert "Lock boostrap-sass to 2.3.0.1 until this issue is fixed - https://github.com/twitter/bootstrap/issues/7118"

Reverting because this causes another issue: https://github.com/twitter/bootstrap/issues/6835
Fixes https://squish.ish.com.au/tasks/view/17768

This reverts commit 73e8523277d6c542b280b479aff573fa853a26e8.