Update to latest Node.js LTS

[DanielBrierton]

As of writing, this is v6.9.5.

Main blocker for this right now is lack of e2e tests. We can't upgrade in confidence that everything still works.

[Wardormeur]

This is a WIP. Version being worked on may differ Done so far :

• [x] cp-orgs (8.x)
• [x] cp-zen-frontend (6.9)

[Wardormeur]

Done since early january