When "git submodule sync" synchronizes the repository URLs
it only updates submodules' .git/config.  However, the old
URLs still exist in the super-project's .git/config.

Update the super-project's configuration so that commands
such as "git submodule update" use the URLs from .gitmodules.
Signed-off-by: NDavid Aguilar <davvid@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>