Fix coverage reports

[kevinbarabash]

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

[lencioni]

Big +1 on moving to jest.

[lencioni]

I think the snapshots would be a great fit for a lot of the current unit tests in particular.