.gitmodules: Change to https:// for crowsfoot submodule
Revert ".gitmodules: Change to https:// for crowsfoot submodule"

This reverts commit 9cfa54f00b7eceedf96b153ad0acb5cdf99f6ca1.

We were trying to solve a problem with Karibe's git repo, but it
seems to be a problem with Ubuntu's gnome-keyring daemon instead
of with the git URLs.