Avoid running tests twice in CI

[JacobBlomgren]

@Dhq and I talked, and travis currently first runs tests, then runs tests again as part of coveralls. I propose that we let test be, for local development, but run it once with nyc in CI. That way we only need to run it once.

[JacobBlomgren]

We will try to convert the whole test codebase to jest instead, circumventing this problem.