Constraint keruald/globalfunctions version in Composer schema

Summary:
Currently we required a minimal version,
we now also cap to 0.9 using tilde operator.

Caret operator isn't needed, lib isn't going to break bc in 0.x,
only to import and tidy up Keruald/Pluton stuff.

Reference: https://getcomposer.org/doc/articles/versions.md#next-significant-release-operators

Fixes T869.

Test Plan: composer validate

Reviewers: dereckson

Maniphest Tasks: T869

Differential Revision: http://devcentral.nasqueron.org/D407