doc: modernize and fix code examples in path.md

Unify spaces, quotes, and semicolons. Update output examples.

PR-URL: https://github.com/nodejs/node/pull/12296


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>