path: fix normalize paths ending with two dots

Fixes: https://github.com/nodejs/security/issues/147
PR-URL: https://github.com/nodejs-private/node-private/pull/94


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Doug Wilson <doug@somethingdoug.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>