R1:d6ed9c2f685a

Fix an undefined variable

Summary: Identifed by linting with JSHint.

Test Plan: `arc lint`

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11433