server: include gitlab raw URLs as git mirrors

server: include gitlab raw URLs as git mirrors

gitlab serves raw files from a CDN, so its appropriate to use the raw URL.
@pserwylo @grote and I discussed it and found a reference, but I can't find
that reference now.

Since the client will try the next mirror if one fails, it makes sense to
include both the gitlab raw and gitlab pages URLs to the mirror.  The
gitlab pages deploy process is still a bit flaky anyway.