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

[yaffs-website] / web / core / modules / system / tests / modules / module_install_class_loader_test2 / module_install_class_loader_test2.info.yml

name: 'Module install class loader test2'
description: 'Support module for tests that the class loader behaves as expected during module install.'
type: module
package: Testing
core: 8.x
version: VERSION
dependencies:
  - drupal:module_install_class_loader_test1