Use correct versions in Composer replace map

Summary:
Versions of the Keruald libraries aren't sync.
As such, it doesn't make sense to use self.version.

Instead, we can read Git tags, and find the greater version
for each package, and use that information as library version.

Test Plan: rm composer.json && make composer.json

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D3224