Stop calling the undefined withIsTag method

Summary: This just cleans up a method call that was missed in D15986. It's been causing fatal errors in one of our workflows.

Test Plan: Grep'd for other instances of withIsTag and didn't find any

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: epriestley, yelirekim

Differential Revision: https://secure.phabricator.com/D17299