Constraint Keruald packages' versions in Composer

Summary:
Packages used unbound versions with >= operator.

We apply a constraint to avoid breaking compatibility.
With such modification, composer.json is now valid.

Fixes T870.

Test Plan: composer validate

Reviewers: dereckson

Subscribers: alken-orin

Maniphest Tasks: T870

Differential Revision: http://devcentral.nasqueron.org/D408