Use Node 6

[macdonst]

Let's just force Node 6 so we can use ES2015 style JS.

[devgeeks]

Yeah, I was tempted. It's really just in the configs etc where it affects things, so I was willing to backpedal that a bit.

6.x is current LTS, but there are probably a lot of users still on older versions...

[devgeeks]

I think it's time to make a call on this and require 6.

[MarcGodard]

I agree.