Travis JWT Addon will be discontinued on April 17, 2018

[vweevers]

See https://blog.travis-ci.com/2018-01-23-jwt-addon-is-deprecated. Need to check what this means for us and our sauce labs CI. I think:

• We need to add credentials to .travis.yml before April 17
• Sauce Labs will no longer be available on PRs 😞

@ralphtheninja, /cc @mcollina