Fix brace formatting linter rule

Summary: Fixes T8847.

Test Plan:
Ran arc lint on a test file:

<?php

if ($x) {
  echo 'foo';
}else {
  echo 'bar';
}

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T8847

Differential Revision: https://secure.phabricator.com/D13633