When setting boolean attributes on Web Components
`<x-search somebool name={this.props.name} />`
they get rendered as attribute/value pairs instead
`<x-search somebool="true" name={this.props.name}>`

This causes problems with some AMP components, for eg. `<amp-iframe />` which has a `resizable` attribute that gets rendered as `resizable="true"`. This results in non valid AMP content and developers crying with blood tears on their keyboards :)
> The attribute 'resizable' in tag 'amp-iframe' is set to the invalid value 'true'. (see https://www.ampproject.org/docs/reference/components/amp-iframe)

Is there any reason for the current behaviour? Will changing this break something else?
it('should warn about props that are no longer supported without case sensitivity (ssr)', () => {
      ReactDOMServer.renderToString(<div />);
      expect(() =>
        ReactDOMServer.renderToString(<div onfocusin={() => {}} />),
      ).toErrorDev(
        'React uses onFocus and onBlur instead of onFocusIn and onFocusOut.',
      );
      expect(() =>
        ReactDOMServer.renderToString(<div onfocusout={() => {}} />),
      ).toErrorDev(
        'React uses onFocus and onBlur instead of onFocusIn and onFocusOut.',
      );
    });
    it('gives source code refs for unknown prop warning', () => {
      expect(() =>
        ReactTestUtils.renderIntoDocument(<div class="paladin" />),
      ).toErrorDev(
        'Warning: Invalid DOM property `class`. Did you mean `className`?\n    in div (at **)',
      );
      expect(() =>
        ReactTestUtils.renderIntoDocument(<input type="text" onclick="1" />),
      ).toErrorDev(
        'Warning: Invalid event handler property `onclick`. Did you mean ' +
          '`onClick`?\n    in input (at **)',
      );
    });
    it('gives source code refs for unknown prop warning (ssr)', () => {
      expect(() =>
        ReactDOMServer.renderToString(<div class="paladin" />),
      ).toErrorDev(