Use long array syntax for compatibility instead of short array syntax

Summary: Fixes T11409. This syntax isn't compatible with older PHP.

Test Plan: Ran arc lint on the file.

Reviewers: yelirekim, chad

Reviewed By: chad

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T11409

Differential Revision: https://secure.phabricator.com/D16358