test: add path.join's test

Add test when the argument is empty.
Adjust the position of the comment.
Make use of Arrow Function, Template Literals and `Array.from`.

PR-URL: https://github.com/nodejs/node/pull/11063


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>