Update Travis to check for changes after regenerating tests

[leobalter]

No description provided.

[leobalter]

Thanks, @tcare!

[jugglinmike]

Unless I am mistaken, this change was made with the expectation that
contributors manually generate tests and submit them as part of the review
process. This is not what I had in mind with gh-546. There, I proposed
deployment logic (which has since been moved to a separate
script)
that would result in the automated introduction of generated files. Note that
the current contribution guidelines read:

Tests expressed with this convention are built automatically following the
source files' acceptance into the project. Patches should not include
assets built from these sources.

So if we want to continue to require contributors to submit
procedurally-generated files, we'll need to change that text (in addition to
removing the deployment logic/key).