Revert "Change submodule URL from git:// to http://"

This reverts commit 19a6e24a11b76049feed76cbc5604a7fcb90ac14.

This was a local experiment that I pushed to Github accidentally.
diff --git a/.gitmodules b/.gitmodules
index f4a246e..8566567 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,3 +1,3 @@
 [submodule "shFlags"]
 	path = shFlags
-	url = https://nvie@github.com/nvie/shFlags.git
+	url = git://github.com/nvie/shFlags.git