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

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

name: 'Off-canvas tests'
type: module
description: 'Provides off-canvas test links.'
package: Testing
version: VERSION
core: 8.x