Update Composer dependency for php-amqplib

Summary:
The Composer package videlalvaro/php-amqplib is superseded
by php-amqplib/php-amqplib.

Fixes T782.

Test Plan: Run tests, see if Notifications center still works

Reviewers: dereckson

Maniphest Tasks: T782

Differential Revision: http://devcentral.nasqueron.org/D339