package/dovecot: security bump to version 2.3.4.1

package/dovecot: security bump to version 2.3.4.1

Fixes the following security issues:

 * CVE-2019-3814: If imap/pop3/managesieve/submission client has
   trusted certificate with missing username field
   (ssl_cert_username_field), under some configurations Dovecot
   mistakenly trusts the username provided via authentication instead
   of failing.

 * ssl_cert_username_field setting was ignored with external SMTP AUTH,
   because none of the MTAs (Postfix, Exim) currently send the
   cert_username field. This may have allowed users with trusted
   certificate to specify any username in the authentication. This bug
   didn't affect Dovecot's Submission service.

For more details, see the announcement:
https://www.dovecot.org/list/dovecot-news/2019-February/000394.html

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>