message: Calculated crumb from key
  If key is 2++ then crumb is 2. Can't use index because when replacing need both scenes (replacer and replacee) to have the same crumb
diff: @@ -75,9 +75,10 @@ class NavigationMotion extends React.Component<NavigationMotionProps, Navigation
  onRest={({key}) => this.clearScene(key)}
  duration={duration}>
  {styles => (
  - styles.map(({data: {key, state, data}, style}, index) => {
  - var scene = <Scene crumb={index} renderScene={renderScene} /> ;
  - return children(style, scene, key, crumbs.length === index, state, data);
  + styles.map(({data: {key, state, data}, style}) => {
  + var crumb = +key.replace(/\+/g, '');
  + var scene = <Scene crumb={crumb} renderScene={renderScene} /> ;
  + return children(style, scene, key, crumbs.length === crumb, state, data);
  }).concat(
  sharedElementMotion && sharedElementMotion({
  key: 'sharedElements',
  