Test in Safari and Edge

[appsforartists]

Travis supports Mac and Linux. Linux is easier to set up, so that's what we currently have; however, there are more browsers available for Mac. Travis doesn't appear to currently support Windows.

Most of what we're writing in Material Motion is pure logic - all the parts that care about a particular DOM implementation should live in streams-dom. It would be reasonable to test the logic once and only have cross-browser testing for streams-dom. Still, I'd rather have robots worry about maintaining cross-browser support than us; hence, we should probably run the whole test suite in at least:

• Chrome
• Safari
• Firefox
• Edge

Since we can't get Edge on Travis alone, we may want to consider using BrowserStack or SauceLabs for cross-browser testing.