package/dovecot: security bump version to 2.3.13

package/dovecot: security bump version to 2.3.13

Updated license hash due to upstream commit:
https://github.com/dovecot/core/commit/bf7952d33e39358a1258697505ed25c050e14bbb

Fixes the following CVEs:

CVE-2020-24386:
https://dovecot.org/pipermail/dovecot-news/2021-January/000450.html

CVE-2020-25275:
https://dovecot.org/pipermail/dovecot-news/2021-January/000451.html

Release notes:
https://dovecot.org/pipermail/dovecot-news/2021-January/000448.html

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