url: restrict setting protocol to "file"

Since file URLs can not have `username/password/port`,
the specification was updated to restrict setting protocol to "file".

Refs: https://github.com/whatwg/url/pull/269
Fixes: https://github.com/nodejs/node/issues/11785
PR-URL: https://github.com/nodejs/node/pull/11887


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>