Use relative URL's all-the-way up to the GitHub root. Benefits:
- Keep the ability to clone using both `ssh` and `https` URLs (for
external developers or the fortunate ones that are working behind
a transparent http proxy)
- Allow forking the project, because later `clone` operation does not
require to have forked every submodule.
Enyo-DCO-1.1-Signed-off-by: Francois-Xavier KOWALSKI <firstname.lastname@example.org>