Upgrade to oik-types v2.0.0-alpha-20181019 for PHP 7.2 support.
oik-types supports peaceful coexistence with WordPress 5 / Gutenberg. It allows you to override post type registrations to either enable or disable the REST API. When the REST API is enabled for a post type and its associated taxonomies then you will be able to use the Block editor.
oik-types v2.0.0-alpha20181019 is dependent upon oik v3.2.3, the minimum version which also supports WordPress 5.0, Gutenberg and PHP 7.2.