- update to node 10
- set maxWorkers on unittests so they don't spawn so many that we run 
out of memory.
- set runInBand on integration tests. There's a weird interaction that 
makes the constumes test or tutorials test fail due to a page crash.

While CircleCI is running in parallel with Travis, let Travis continue to handle the deployments.

The requirements for npm publishing and gh-pages are different anyway.

The equivalent config for Travis is only 87 lines long, and easy to read. Can CircleCI be similarly easy to read? Is this easy? Are you still reading this?

They show up as errors

NODE_ENV isn’t one we’d want to change dynamically, so keep it checked in to the config