message: Used single field to track event
  No need for peek and peekEvent
diff: @@ -91,8 +91,7 @@ class Scene extends React.Component<SceneProps, SceneState> {
  static createStateContext(crumbs: Crumb[], nextCrumb: Crumb, crumb: number, navigationEvent: NavigationEvent) {
  var stateContext = new StateContext();
  var {state, data, url, title} = crumbs[crumb];
  - stateContext['peek'] = true;
  - stateContext['peekEvent'] = navigationEvent;
  + stateContext['peek'] = navigationEvent;
  stateContext.state = state;
  stateContext.data = data;
  stateContext.url = url;
  @@ -143,7 +142,7 @@ class Scene extends React.Component<SceneProps, SceneState> {
  <BackButton onPress={this.handleBack} />
  <NavigationContext.Provider value={navigationEvent}>
  <Freeze freeze={freezable && crumbs.length !== crumb && navigationEvent
  - && (!stateContext['peek'] || stateContext['peekEvent'] !== this.props.navigationEvent)}>
  + && (!stateContext['peek'] || stateContext['peek'] !== this.props.navigationEvent)}>
  <NVFreeze style={styles.scene}>
  {navigationEvent && this.props.renderScene(state, data)}
  </NVFreeze>
  