Updated Drupal to 8.6. This goes with the following updates because it's possible...

[yaffs-website] / vendor / chi-teck / drupal-code-generator / templates / d8 / plugin-manager / yaml / model.services.yml.twig

services:
  plugin.manager.{{ plugin_type }}:
    class: Drupal\{{ machine_name }}\{{ class_prefix }}PluginManager
    arguments: ['@module_handler', '@cache.discovery']