No Roots

I defined a RootStore, but get the "No Roots" message here in mobx-devtools. Everything seems to be working with a mix of class and functional components.

```
const store = RootStore.create(); // from HO
makeInspectable(store);
window.z = store; // for console debugging

ReactDOM.render(
  <Provider store={store}>
    <App />
  </Provider>,
  document.getElementById("root")
);

```

