MAINTAINERS: nilfs2: update email address

Change my email since lab.ntt.co.jp email domain has been deprecated due
to company policy.

Link: http://lkml.kernel.org/r/1562495153-8166-1-git-send-email-konishi.ryusuke@gmail.com


Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>