Squashed 'rbenv/plugins/ruby-build/' changes from 3545e25..3190b36

3190b36 Merge pull request #612 from sstephenson/git-revision
daee882 Faster clone of Bats in CI
e8e77e6 Read ruby-build revision from git if available

git-subtree-dir: rbenv/plugins/ruby-build
git-subtree-split: 3190b36fdbc0a2f6130b8ce5489d106665ce685c
Merge commit '2f53b3c0718c377c92d169142537e1ede8a256f3'

Pull sstephenson/ruby-build