no issue
- updates `@tryghost/url-utils` following an internal refactor of the package
- renames `makeAbsoluteUrls` to `htmlRelativeToAbsolute` to better reflect what the function is doing
- renames `getBlogUrl` to `getSiteUrl`
- updates UrlUtils test stubbing util to work with a class
- fixes use of invalid port numbers in tests (max port number is 65535, any higher is an invalid URL that will error with some parsers)