Remove an unnecessary default argument
Mirrors

Not sure if you prefer one commit per mirror change, if so let me know
and I’ll re-do this.

Adds a new mirror to counter various gnu formula rejecting an awful lot
of connections through proxies/unusual routing/etc. Debian would be the
perfect mirror, but the way they deal with updating packages makes this
option unavailable a lot of the time alas.
gnupg: update 1.4.18 bottle.
gnupg2: update 2.0.26 bottle.
libassuan: update 2.1.2 bottle.