package/dovecot-pigeonhole: bump version to 0.5.21
Release notes:
https://dovecot.org/mailman3/archives/list/dovecot-news@dovecot.org/thread/Y5SJWAIAVEAQ2KKSWJM7VSJUUFRMFAH5/
Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>