Update Saucelabs credentials

[m-mujica]

Currently using the ones from Steal which is messing up the matrix on the readme page.

[m-mujica]

we still need to fix this

[m-mujica]

This is how Steal's matrix looks right now because of some broken steal-css build.

@matthewp were you able to create the account for steal-css? I can't remember what was the problem

I'm going to merge one of the greenkeeper PRs in steal to trigger a new build, hopefully that fixes the matrix.