Internal: Replace Node 5 by Node 6 on CI

[MoOx]

Blocked by :

• Node.js 6.0.0 appveyor/ci#770
• Add support for Node.js 6 tschaub/mock-fs#106

[tschaub]

If you upgrade to mock-fs@3.9.0, you should be able to polish this off.

[MoOx]

Now it's seems that linked webpack is causing the issue (the error comes from the fact that 2 webpacks deps are used, if my memory is correct, that why we use symlink, due to the fact that our test are run in a subfolder, and not a parent folder, like in real life).

[thangngoc89]

Yeah. I know. I suppose because of the way node 6 resolve dependencies.