Runs our espresso tests on Travis.

[rjrjr]

Addressing #242

[rjrjr]

The before_install: block might be redundant. Will try w/o before merging.

[rjrjr]

Cool, an actual failure. :/ Working on that.

Should also look into parallel unit and integration test builds, to keep PR feedback loop tight. https://docs.travis-ci.com/user/speeding-up-the-build/

[rjrjr]

Fixed the embarrassment, and now seeing the usual Espresso Tests are Flakey misery. I'll dig into that a bit. Might have to back off to adding a line to RELEASING.md reminding us to run the things manually.

[rjrjr]

flow.sample.tree.TreeSampleTest#editsAreSaved is flaky. So far only seen it fail when all tests are run, so it comes up after the orientation lock test in MultiKeySampleTest#walkthrough. Not at all certain the orientation lock is actually related, just pointing out the ordering.

[rjrjr]

Can reproduce by running the TreeSampleTest itself repeatedly, not a side effect of any other tests. E.g.

  @Test public void one() {
    editsAreSaved();
  }

  @Test public void two() {
    editsAreSaved();
  }

  @Test public void three() {
    editsAreSaved();
  }