Fix coverage reports

I'm not sure why coveralls is report 0% coverage. It might have to do with using `@babel/register`. I was thinking we might look at moving to `jest` which also produces coverage reports doesn't require `@babel/register` to run ES6. I was also thinking of maybe using codecov.io for tracking coverage as it provides reports inside PRs. I'm not sure if coveralls does that. The current coverage has been broken for a while so starting fresh doesn't seem so bad. https://coveralls.io/github/Khan/aphrodite?branch=master

Start with the current Coveralls report and the @babel/register setup, then investigate the existing coverage flow and the proposed Jest or Codecov alternatives. Done means coverage is generated reliably and published with a clear, working tracking approach.

Written by the indexing model from the issue text.