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?
spyOnDevAndProd(container.firstChild, 'setAttribute');
      ReactDOM.render(<progress value={30} />, container);
      ReactDOM.render(<progress value="30" />, container);
      expect(container.firstChild.setAttribute).toHaveBeenCalledTimes(2);
    });
    it('should return the progress to intermediate state on null value', () => {
      const container = document.createElement('div');
      ReactDOM.render(<progress value={30} />, container);
      ReactDOM.render(<progress value={null} />, container);
      
      
      expect(container.firstChild.hasAttribute('value')).toBe(false);
    });
    
    it('custom element custom events lowercase', () => {
      const oncustomevent = jest.fn();
      function Test() {
        return <my-custom-element oncustomevent={oncustomevent} />;
      }
      const container = document.createElement('div');
      ReactDOM.render(<Test />, container);
      container
        .querySelector('my-custom-element')
        .dispatchEvent(new Event('customevent'));
      expect(oncustomevent).toHaveBeenCalledTimes(1);
    });
    
    it('custom element custom events uppercase', () => {
      const oncustomevent = jest.fn();
      function Test() {