message: Detaulted to state title only if no title prop
diff: @@ -13,7 +13,7 @@ class Scene extends React.Component<SceneProps, SceneState> {
  this.onWillAppear = this.onWillAppear.bind(this);
  }
  static defaultProps = {
  - title: () => null,
  + title: (state: State) => state.title,
  renderScene: (state: State, data: any) => state.renderScene(data)
  }
  static getDerivedStateFromProps(props: SceneProps) {
  @@ -92,7 +92,7 @@ class Scene extends React.Component<SceneProps, SceneState> {
  var {state, data} = (crumb < crumbs.length) ? crumbs[crumb] : nextCrumb;
  return (
  <NVScene
  - title={title(state, data) || state.title}
  + title={title(state, data)}
  style={styles.scene}
  onWillAppear={this.onWillAppear}>
  <NavigationContext.Provider value={navigationEvent}>
  