<label for="foo"> isn't followed on IE

[AlexLloyd0]

17/116 unit tests currently fail on Internet Explorer.

e.g.

  fit('understands label for', () => {
    render(
        html`
    <button id="foo">text</button>
    <label for="foo">bar</label>`,
        container);
    const elem = document.getElementById('foo');
    expect(computeTextAlternative(elem!)).toBe('bar');
  });

This passes on chrome and firefox but IE gives elem an accessible name of text.