Upgrade to Laravel 5.3

Summary:
This change offers an incremental framework upgrade from 5.2 to 5.3.

The last 5.x version is 5.8, and Laravel 6 has been released,
but as the Laravel documentation offers migration paths by
minor version, upgrades will be incremental.

Reference: https://laravel.com/docs/5.3/upgrade

Ref T1484.

Test Plan: The test suite pass.

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1484

Differential Revision: https://devcentral.nasqueron.org/D2129