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

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

name: Test features
type: theme
core: 8.x
description: 'Test theme to test theme settings with limited features.'
features:
  - node_user_picture
  - comment_user_picture
  - comment_user_verification