Fix URI for Phurl NUX

Summary: Fixes T11685. We missed this one straggler the recent conversion of Phurl to EditEngine, in T10673.

Test Plan: Visited /phurl/?nux=1, clicked "Shorten a URL".

Reviewers: chad, jcox

Reviewed By: jcox

Maniphest Tasks: T11685

Differential Revision: https://secure.phabricator.com/D16587