versions: Update PHP dependencies for Master to 7.2

Once https://tracker.moodle.org/browse/MDL-65809 is integrated, master will stop working with PHP 7.1, as far as 7.2 is the new requirement there.

We need to configure Versions here (Master) to be aware of that, that way, any jobs using the "LOWER" PHP version supported will, automatically switch from PHP 7.1 to 7.2