Update Jest to 16

[gaearon]

Jest released an update this week.

We need to bump the versions of any Jest packages we are using, and also clean up any configuration options that are no longer necessary (e.g. I think we can now remove the test file regex because Jest finds JSX files by default now).

This is up for grabs. If you plan to work on it please comment here so we don’t duplicate work.

[chase]

If nobody has claimed this elsewhere, I could give it a shot. Seems simple enough :)

[gaearon]

Sounds good, you got it!