message: Rendered App if single root
  App defaults to Scene
diff: @@ -56,7 +56,7 @@ class NavigationMotion extends React.Component<NavigationMotionProps, Navigation
  return typeof styleProp === 'function' ? styleProp(state, data, crumbs, nextState, nextData) : styleProp;
  }
  render() {
  - var {children, duration, app, rootPerScene, sharedElementMotion, stateNavigator} = this.props;
  + var {children, duration, app: App, rootPerScene, sharedElementMotion, stateNavigator} = this.props;
  var {stateContext: {crumbs, oldState}, stateContext} = stateNavigator;
  return (stateContext.state &&
  <SharedElementContext.Provider value={this.sharedElementRegistry}>
  @@ -70,7 +70,7 @@ class NavigationMotion extends React.Component<NavigationMotionProps, Navigation
  duration={duration}>
  {styles => (
  styles.map(({data: {key, state, data}, style}) => {
  - var scene = !rootPerScene ? <Scene crumb={key} /> : <SceneProxy crumb={key} app={app} />;
  + var scene = !rootPerScene ? <App crumb={key} /> : <SceneProxy crumb={key} app={App} />;
  return children(style, scene, key, crumbs.length === key, state, data);
  }).concat(
  sharedElementMotion && sharedElementMotion({
  