message: Comapred props directly
  The instance variable didn't add anything because the crumbs prop now holds the index
diff: import * as React from 'react';
  class Scene extends React.Component<any, any> {
  - private index: number;
  - constructor(props) {
  - super(props);
  - this.index = props.crumbs;
  - }
  shouldComponentUpdate(props) {
  - return this.index === props.stateNavigator.stateContext.crumbs.length;
  + return props.crumbs === props.stateNavigator.stateContext.crumbs.length;
  }
  render() {
  return this.props.children;
  