package/dovecot-pigeonhole: bump version to 0.5.16
Release notes:
https://dovecot.org/pipermail/dovecot-news/2021-August/000464.html
Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>