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

[yaffs-website] / web / core / modules / contextual / tests / modules / contextual_test / contextual_test.links.contextual.yml

contextual_test:
  title: 'Test Link'
  route_name: 'contextual_test'
  group: 'contextual_test'
contextual_test_ajax:
  title: 'Test Link with Ajax'
  route_name: 'contextual_test'
  group: 'contextual_test'
  options:
    attributes:
      class: ['use-ajax']
      data-dialog-type: 'modal'