Update links to legal references

Summary:
Guide des citations, reférences et abréviations juridiques

Same than in 5b7113ef3a81, but pointing this time to UNamur web site,
as it doesn't seem to be available on the new Kluwers website.

Copyright Term and the Public Domain in the United States

The Cornell University Library updated site structure.

Test Plan: Check new URL

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D2564