download.civicrm.org: upgrade to PHP 7.3
- Currently runs PHP 5.6
- Service is on www-prod.c.o.o, which runs also PHP 7.3 for docs (running as php-fpm, so both can co-exist).
https://github.com/civicrm/civicrm-upgrade-manager
See also #907
https://github.com/civicrm/civicrm-upgrade-manager
See also #907