update net-im/prosody to 0.9.12

http://blog.prosody.im/prosody-0-9-11-released/
http://blog.prosody.im/prosody-0-9-12-released/

PR: 214487
Submitted by: Piotr Kubaj <pkubaj@anongoth.pl>
Reviewed by: matthew
Approved by: matthew (mentor), lx (maintainer)
Differential Revision: https://reviews.freebsd.org/D9328