Minor fix for the `ArcanistXHPASTLinter`.

Summary: This `LINT_PHP_53_FEATURES` should have been replaced with `LINT_PHP_COMPATIBILITY` in D9576.

Test Plan: Ran `arc unit`.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9655