Vue-test-utils: Move to Circle 2.0

[eddyerburgh]

What problem does this feature solve?

At the moment we're using Circle 1.0, which isn't supported from August 2018

What does the proposed API look like?

We should move to circle 2.0, and parallelize the compatability tests—https://github.com/vuejs/vue-test-utils/blob/dev/scripts/test-compat.sh

[probil]

Resources and guides to help you make the transition https://circleci.com/sunset1-0/

[eddyerburgh]

We're using circle 2 now, but the tests aren't paralellized—https://github.com/vuejs/vue-test-utils/blob/dev/.circleci/config.yml