Stablize omnitools library version
The Keruald OmniTool library at 0.2.0 version contains all the functions
previously contained in this library.
As such, this becomes the minimal version to require. As OmniTool adheres
to semantic versionning, there is a choice between ~0.2 (0.2.*) and ^0.2 (0.*).
As 0.3 will be used to add new functions more than refactor the existing ones,
the caret operator seems more convenient.
Test Plan: composer validate
Reviewed By: dereckson
Maniphest Tasks: T1395
Differential Revision: https://devcentral.nasqueron.org/D1626