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

[yaffs-website] / web / core / modules / contact / tests / modules / contact_storage_test / contact_storage_test.info.yml

name: 'Contact test storage'
type: module
description: 'Tests that contact messages can be stored.'
package: Testing
version: VERSION
core: 8.x
dependencies:
  - drupal:contact
  - drupal:user