Update comment to reflect a directory's new name.

Bug: chromium:1133549
Change-Id: I7140370746acd9bfa8b5e90257a61effbb72b97e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3068888
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Gavin Mak <gavinmak@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>

git_cl.py

@@ -5292,7 +5292,7 @@ def CMDformat(parser, args):
       #   $ python pretty_print.py
       # But in tools/metrics/histogrmas, pretty-print should be run with an
       # additional relative path argument, like:
-      #   $ python pretty_print.py histograms_xml/UMA/histograms.xml
+      #   $ python pretty_print.py metadata/UMA/histograms.xml
       #   $ python pretty_print.py enums.xml
 
       # TODO (crbug/1116488): Remove this check after ensuring that the updated