Update to use CircleCI version 2.

[gitlost]

See wp-cli/scaffold-command#115

Should update to use CircleCI Version 2.

[Daniel Bachhuber]

This will need to happen sooner, because CircleCI 1.0 is sunsetting.

[Alain Schlesser]

Oh, this was already completed (the above PR is merged), we just didn't close off the corresponding issue.

[Daniel Bachhuber]

@schlessera This repo still looks like v1: https://github.com/wp-cli/scaffold-package-command/blob/master/circle.yml

I think you're referring to the other.

[Alain Schlesser]

Ah, nevermind, I misread. This is for the scaffold package command.