Hi; You’re right always to look closely 
Unfortunately I’m not able to find it …
Anyway, the changes are already online, so it went straight forward with this:
cd /var/www/owncloud/
rm lib/composer/sabre/dav/lib/CardDAV/Plugin.php
cd lib/composer/sabre/dav/lib/CardDAV/
wget https://github.com/sabre-io/dav/raw/master/lib/CardDAV/Plugin.php
Now I’m back in business; Thank you! 