This adds a compatibility shim for the new namespaced structure of PHPUnit and the removed `setExpectedException()` method. In addition, this updates the Travis config so PHPUnit 6.1 is used where appropriate.
Props miyauchi, gitlost.
Fixes#39822
git-svn-id: https://develop.svn.wordpress.org/trunk@40536 602fd350-edb4-49c9-b593-d223f7449a82