enzyme: hasClass does not work on root ReactWrapper

I think this is because MountedTraversal#instHasClassName short circuits to false if the instance does not pass the isDOMComponent check. Could we relax the check?

Example test case (React 0.14):

const shallowComponent = shallow(<Video src="example.mp4" />);
const mountComponent = mount(<Video src="example.mp4" />);

// From ShallowTraversal
// Works!
assert.equal(shallowComponent.node.props.className, 'Video');

// Works!
assert.isTrue(shallowComponent.hasClass('Video'));

// Fails :( because isDOMComponent(mountComponent.node) is false
// Would otherwise pass
assert.isTrue(mountComponent.hasClass('Video'));

// From MountedTraversal (without isDOMComponent check)
// Works!
assert.equal(findDOMNode(mountComponent.node).className, 'Video');

// Works! ... but seems unnecessary
assert.isTrue(mountComponent.find('.Video').hasClass('Video'));