git_cl: prepend http for go link

This allows users to click the URL from terminal.

Change-Id: I0b5c2b9d5a8221c41d5152b529edcf82f97464c8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4969974
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Josip Sokcevic <sokcevic@chromium.org>

git_cl.py

@@ -5073,7 +5073,7 @@ def CMDupload(parser, args):
             'branches that have un-uploaded updates.\n'
             'Patches can now be reapplied with --force:\n'
             '`git cl patch --reapply --force`.\n'
-            'Googlers may visit go/stacked-changes-dogfood for more information.\n'
+            'Googlers may visit http://go/stacked-changes-dogfood for more information.\n'
             '\n'
             'Depot Tools no longer sets new uploads to "WIP". Please update the\n'
             '"Set new changes to "work in progress" by default" checkbox at\n'