mirrors.magcast.co: add http version to fix redirect issue

mirrors.magcast.co: add http version to fix redirect issue

We need to add a Grml-http version, otherwise we get:

| % bin/masterlist2mirmon Mirrors.masterlist
| [...]
| NL rsync://mirror.serverion.com/grml/
| Use of uninitialized value in printf at bin/masterlist2mirmon line 32, <$fh> line 220.
| DE http://mirrors.magcast.co/
| [...]

While it's supposed to report:

  DE http://mirrors.magcast.co/Linux/grml/

Given that there's a http mirror available (which redirects to https)
let's add it accordingly, then the mirrors.magcast.co mirror behaves as
expected and doesn't end up with URLs like
https://mirrors.magcast.co//SHA256SUMS which obviously don't exist as
such.

Thanks: Christopher Bock for reporting and assistance in debugging