Testing enhancements

[ghost]

• [ ] Ensure the Newton command-line adapter works with Nashorn.
• [ ] Add Nashorn to the test matrix.
• [ ] Merge #49; update our list of supported environments to match those provided by Sauce.
• [ ] Switch to the new Travis container-based infrastructure.
• [ ] Add Browserify, webpack, and r.js integration tests
• [ ] Improve the noConflict and runInContext tests. a7f5fe8bc078f3c67fd24b696847bb8a74a2e34f fixed a regression where runInContext would return early for environments that supported JSON natively, but this wasn't caught by the tests.