kanboard: Disable HSTS in app

The HSTS header is already added by nginx. If kanboard adds its own the
reply contains a header that contains max-age twice which is invalid.
Signed-off-by: Florian Pritz <bluewind@xinu.at>

roles/kanboard/templates/config.php.j2

@@ -5,3 +5,5 @@ define('DB_USERNAME', '{{kanboard_db_user}}');
 define('DB_PASSWORD', '{{kanboard_db_password}}');
 define('DB_HOSTNAME', 'localhost');
 define('DB_NAME', '{{kanboard_db}}');
+
+define('ENABLE_HSTS', false);