Update Mocha

[RobLoach]

It's really old.

[willrowe]

It would probably be a good idea to review and update all dependencies for an upcoming release. Do you think there would be any issues with doing so on a minor release or would a major release be safer?

[RobLoach]

I tried a bit, and got some conflicts. I'd be fine with a minor release. Have some time available this week to help out too.