git submodule URL change

FYI if you have an existing Bro git repo clone and want to update/pull
the master branch and all submodules recursively, it will require
syncing one time:

  git submodule sync --recursive

That will update the URL for a git submodule that just changed.
Afterwards, the usual update command will work:

  git submodule update --recursive --init

New git clones Just Work.

- Jon