package/dovecot-pigeonhole: security bump version to 0.5.7.2

Release notes:
https://dovecot.org/pipermail/dovecot/2019-August/116876.html



Fixes
* CVE-2019-11500: ManageSieve protocol parser does not properly handle
  NUL byte when scanning data in quoted strings, leading to out of
  bounds heap memory writes. Found by Nick Roessler and Rafi Rubin.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>