Fix tests (#96)

Closes #63

- Switch from testling to jsdom for browser APIs
- Switch from coverify to nyc for coverage reports
- Clean up related dead code and tooling
- Update Travis to use Node v6 and v8, since we need ES6 features for jsdom.

tests/lib/events.js

@@ -102,7 +102,8 @@ tape("test events on top level elements", function(t) {
   el = window;
 
   el.className = ""
-  on(el, "click", classCb)
+  // With jsdom, the default this is global, not window, so we need to explicitly bind to window.
+  on(el, "click", classCb.bind(window))
   trigger(el, "click")
   t.equal(el.className, "on", "attached callback has been fired properly on window")