Fix a missing space in message.

Change-Id: Ife904f3c43197574b8dcd74dccdeea5f7120534c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5230259
Auto-Submit: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Gavin Mak <gavinmak@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>

gclient.py

@@ -2935,7 +2935,7 @@ def CMDgitmodules(parser, args):
     if cache_info:
         subprocess2.call(['git', 'update-index', '--add'] + cache_info)
     subprocess2.call(['git', 'add', '.gitmodules'])
-    print('.gitmodules and gitlinks updated. Please check `git diff --staged`'
+    print('.gitmodules and gitlinks updated. Please check `git diff --staged` '
           'and commit those staged changes (`git commit` without -a)')