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

[yaffs-website] / vendor / symfony / dependency-injection / Tests / Fixtures / yaml / services2.yml

parameters:
    foo: bar
    values:
        - true
        - false
        - 0
        - 1000.3
        - !php/const PHP_INT_MAX
    bar: foo
    escape: '@@escapeme'
    foo_bar: '@foo_bar'
    mixedcase:
        MixedCaseKey: value