package/dovecot: security bump version to 2.3.7.2

Release notes:
https://dovecot.org/pipermail/dovecot/2019-August/116874.html



Fixes
* CVE-2019-11500: IMAP 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>