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

[yaffs-website] / vendor / chi-teck / drupal-code-generator / templates / d7 / hook / aggregator_fetch.twig

/**
 * Implements hook_aggregator_fetch().
 */
function {{ machine_name }}_aggregator_fetch($feed) {
  $feed->source_string = mymodule_fetch($feed->url);
}