www/seahub: pass MAINTAINER to submitter

Reference: https://lists.freebsd.org/pipermail/freebsd-ports/2015-October/100923.html

PR: 204110
Approved by: Jingfeng Yan <yan_jingfeng@yahoo.com> (outgoing maintainer)
Submitted by: Ricky Gallamore <ultima1252@gmail.com>