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

[yaffs-website] / web / core / modules / migrate / tests / modules / migrate_high_water_test / migrate_high_water_test.info.yml

type: module
name: Migration High Water Test
description: 'Provides test fixtures for testing high water marks.'
package: Testing
core: 8.x
dependencies:
  - drupal:migrate