Merge pull request #3416 from zmwangx/bump-formula-pr-fix-message

bump-formula-pr: --message: add newlines before and after hr

Author: MikeMcQuaid

Library/Homebrew/dev-cmd/bump-formula-pr.rb

@@ -346,8 +346,9 @@ def bump_formula_pr
         EOS
         user_message = ARGV.value("message")
         if user_message
-          pr_message += <<~EOS
+          pr_message += "\n" + <<~EOS
             ---
+
             #{user_message}
           EOS
         end