Fix lint errors found by Nemo

Summary:
See also:

• https://github.com/tpyo/amazon-s3-php-class/pull/33
• https://github.com/stripe/stripe-php/pull/13

Test Plan: Ran a script analyzing sources by HPHP.

Reviewers: btrahan, jungejason, epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D2713