Use https for submodule

The git protocol provides no transport security. https does provide
transport security and should be preferred by default. https is also
more likely than git to be permitted by firewalls in restricted
environments.

Signed-off-by: Daniel M. Weeks <dan@danweeks.net>

.gitmodules

@@ -1,3 +1,3 @@
 [submodule "git"]
-	url = git://git.kernel.org/pub/scm/git/git.git
+	url = https://git.kernel.org/pub/scm/git/git.git
 	path = git