def clean_all
      (review_branches - protected_branches).each do |branch_name|
        # only clean up obsolete branches.
        delete_branch(branch_name) unless unmerged_commits?(branch_name, false)
      end
    end
def clean_all
      (review_branches - protected_branches).each do |branch_name|
        # only clean up obsolete branches.
        delete_branch(branch_name) unless unmerged_commits?(branch_name, false)
      end
    end
clean all obsolete branches