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

[yaffs-website] / web / modules / contrib / fontyourface / fontyourface.services.yml

services:
  asset.css.MISSPELLEDcollection_renderer:
    class: Drupal\fontyourface\Asset\FontYourFaceInlineCssCollectionRenderer
    arguments: [ '@state' ]