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

[yaffs-website] / vendor / consolidation / site-alias / tests / fixtures / sitealiases / dup / single.site.yml

default: dev
dev:
  root: /dup/path/to/single
alternate:
  root: /dup/alternate/path/to/single
common:
  foo: dup