Administration - Installation - Core: ILIAS 6.8 : Setup Parse error class.ilUserPasswordEncoderFactory.php on line 74

Hello,

During an upgrade from version 5.3 to version 6.8 we encounter the following error:
Parse error: syntax error, unexpected '?' in /var/www/html/ilias/Services/User/classes/class.ilUserPasswordEncoderFactory.php on line 74

1. We have installed the system recommendations on our server (versions... PHP, WKHTMLTOPDF, ...)


2. We have downloaded the TAR.GZ from ilias.de (ilias 6.8)


3. We have saved our "ilias.ini.php"


4. We installed the downloaded version 6.8.


5. We repositioned "ilias.ini.php".


6. We set the "chown" rights on ilias.


7. We launched http://xxxxxxx/setup/setup.php

We get the following error: 
Parse error: syntax error, unexpected '?' in /var/www/html/ilias/Services/User/classes/class.ilUserPasswordEncoderFactory.php on line 74

Thank you for your help, cordially,