Add PSR-3 log implementation to phan configuration

Summary:
This fixes the following issue detected by phan:

app/Exceptions/Handler.php:49
PhanUndeclaredClassMethod
Call to method error from undeclared class \Psr\Log\LoggerInterface

Test Plan: phan | grep Psr

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D779