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

[yaffs-website] / web / core / modules / field / tests / modules / field_test / field_test.info.yml

name: 'Field API Test'
type: module
description: 'Support module for the Field API tests.'
core: 8.x
package: Testing
version: VERSION
dependencies:
  - drupal:entity_test