Upgrade to PHP 5.6.27

Summary: Resolves T1032

Test Plan: Rebuild the image's tags on Dwellers, `php -i```

Reviewers: Sandlayth, dereckson

Subscribers: Nasqueron Docker deployment squad

Tags: Docker images

Maniphest Tasks: T1032

Differential Revision: https://devcentral.nasqueron.org/D688