yew 0.20.0 version changes

[ztuskes]

I just leave here if someone try the example, but want use the later version of yew:

yew::start_app::<CounterComponent>();

changed to:

yew::Renderer::<CounterComponent>::new().render();

[aplatypus]

Yes that fixes the problem. I think the example should be updated to match currently supported Yew features.