Include branch name in git-squash-branch's default message

Change-Id: I5dfa6017d1c938f8e1c55fbd6e607909aa4d6811
Reviewed-on: https://chromium-review.googlesource.com/422589
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Alan Cutter <alancutter@chromium.org>
diff --git a/git_squash_branch.py b/git_squash_branch.py
index 33366d2..f0534ca 100755
--- a/git_squash_branch.py
+++ b/git_squash_branch.py
@@ -11,7 +11,7 @@
 def main(args):
   parser = argparse.ArgumentParser()
   parser.add_argument(
-      '-m', '--message', metavar='<msg>', default='git squash commit.',
+      '-m', '--message', metavar='<msg>', default=None,
       help='Use the given <msg> as the first line of the commit message.')
   opts = parser.parse_args(args)
   if git_common.is_dirty_git_tree('squash-branch'):