add AAAA record for phabricator

to enable IPv6 for phabricator as requested in:

https://phabricator.wikimedia.org/T509

misc-web-lb.eqiad already has this:

misc-web-lb.eqiad.wikimedia.org. 3599 IN AAAA	2620:0:861:ed1a::11

Change-Id: Ie000784baa3c7079983f3dc3f8b2bae839c2e502