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

[yaffs-website] / vendor / symfony / routing / Tests / Fixtures / validresource.yml

_blog:
    resource:     validpattern.yml
    prefix:       /{foo}
    defaults:     { 'foo': '123' }
    requirements: { 'foo': '\d+' }
    options:      { 'foo': 'bar' }
    host:         ""
    condition:    'context.getMethod() == "POST"'