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

This makes it easy to download the submodule from behind a corporate
firewall.
diff --git a/.gitmodules b/.gitmodules
index 8566567..f4a246e 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,3 +1,3 @@
 [submodule "shFlags"]
 	path = shFlags
-	url = git://github.com/nvie/shFlags.git
+	url = https://nvie@github.com/nvie/shFlags.git