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

[yaffs-website] / web / core / modules / system / tests / modules / form_test / form_test.info.yml

name: 'FormAPI Test'
type: module
description: 'Support module for Form API tests.'
package: Testing
version: VERSION
core: 8.x
dependencies:
  - file
  - filter