Change double quotes to single quotes in JavaScript.

Summary: As advised by JSHint.

Test Plan: I'm not really sure how to comprehensively test this. It looks okay to me.

Reviewers: chad, epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9677