R1:48569f3629b2

Minor change to suppress linter warning

Summary: Explicitly declare the delimiter for `preg_quote`.

Test Plan: `arc lint`

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11914