Editorial: align with URL's cannot-be-base-URL removal (#143)
* Editorial: align with URL's cannot-be-base-URL removal
These URLs now have a path whose value is a string rather than a list.
See https://github.com/whatwg/url/pull/655 for context.
* Apply suggestions from code review
Co-authored-by: Anne van Kesteren <annevk@annevk.nl>
Co-authored-by: Ben Kelly <ben@wanderview.com>