package/dovecot: security bump version to 2.3.15

Fixes several security bugs:

CVE-2021-29157
- https://dovecot.org/pipermail/dovecot-news/2021-June/000461.html

CVE-2021-33515
- https://dovecot.org/pipermail/dovecot-news/2021-June/000462.html

Release notes:
https://dovecot.org/pipermail/dovecot-news/2021-June/000457.html

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
(cherry picked from commit c711012fa5aea8c3cb9f6fb2470d7b9be849db40)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/dovecot/dovecot.hash

@@ -1,5 +1,5 @@
 # Locally computed after checking signature
-sha256  c8b3d7f3af1e558a3ff0f970309d4013a4d3ce136f8c02a53a3b05f345b9a34a  dovecot-2.3.14.tar.gz
+sha256  21bbdd5d45957a99133de8b7e71813ecb73d9476c89dfc63479e9102b3553590  dovecot-2.3.15.tar.gz
 sha256  319a9830aab406109cd67cb45496587566a8123203d66d037b209ca3e13de02a  COPYING
 sha256  dc626520dcd53a22f727af3ee42c770e56c97a64fe3adb063799d8ab032fe551  COPYING.LGPL
 sha256  52b8c95fabb19575281874b661ef7968ea47e8f5d74ba0dd40ce512e52b3fc97  COPYING.MIT

package/dovecot/dovecot.mk

@@ -5,7 +5,7 @@
 ################################################################################
 
 DOVECOT_VERSION_MAJOR = 2.3
-DOVECOT_VERSION = $(DOVECOT_VERSION_MAJOR).14
+DOVECOT_VERSION = $(DOVECOT_VERSION_MAJOR).15
 DOVECOT_SITE = https://dovecot.org/releases/$(DOVECOT_VERSION_MAJOR)
 DOVECOT_INSTALL_STAGING = YES
 DOVECOT_LICENSE = LGPL-2.1, MIT, Public Domain, BSD-3-Clause, Unicode-DFS-2015