git-map: use committer date instead of author date

TBR=iannucci@chromium.org

Change-Id: I07668787e4f26bc4809ea3c3a5331a259655d2da
Reviewed-on: https://chromium-review.googlesource.com/527295
Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Aaron Gable <agable@chromium.org>

git_map.py

@@ -66,7 +66,7 @@ def main(argv):
     return 0
 
   map_extra = get_config_list('depot_tools.map_extra')
-  fmt = '%C(red bold)%h%x09%Creset%C(green)%d%Creset %C(yellow)%ad%Creset ~ %s'
+  fmt = '%C(red bold)%h%x09%Creset%C(green)%d%Creset %C(yellow)%cd%Creset ~ %s'
   log_proc = subprocess2.Popen(
     [GIT_EXE, 'log', '--graph', '--branches', '--tags', root(),
      '--color=always', '--date=short', ('--pretty=format:' + fmt)