MAINTAINERS: add maintainer for replication

As per Stefan's suggestion, add Wen and I as co-maintainers
of replication.

Cc: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: Changlong Xie <xiecl.fnst@cn.fujitsu.com>
Message-id: 1469602913-20979-13-git-send-email-xiecl.fnst@cn.fujitsu.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>