Update screenshot

[vweevers]

A request from Sauce Labs:

If possible, it would be great if you could also update this screenshot to reflect our current branding:

[vweevers]

How about we replace this with a live status matrix, like the one in memdown#browser-support? And add a note saying "airtap itself is tested on Sauce Labs".

[ralphtheninja]

Good idea! Eat your own dogfood :)

[vweevers]

Or maybe not, because our test suite also tests failures. Our build is passing, but it doesn't look like it 😄

[vweevers]

Once memdown is using airtap, we can replace the browser matrix with a screenshot of one of memdown's build jobs.

[ralphtheninja]

@vweevers Once level.js is incorporated into level we could replace memdown with level.