message: Added keys prop so url ones aren't needed
  The keys prop represents the stack. It will change every navigation so no need to force the change with url props
diff: @@ -84,13 +84,12 @@ class NavigationStack extends React.Component<NavigationStackProps, NavigationSt
  render() {
  var {keys, finish} = this.state;
  var {stateNavigator, title, renderScene} = this.props;
  - var {url, oldUrl, crumbs, nextCrumb} = stateNavigator.stateContext;
  + var {crumbs, nextCrumb} = stateNavigator.stateContext;
  var scenes = crumbs.concat(nextCrumb).map((crumb, index) => ({crumb, key: keys[index]}));
  return (
  <NVNavigationStack
  ref={this.ref}
  - url={url}
  - oldUrl={oldUrl}
  + keys={keys}
  finish={finish}
  style={styles.stack}
  {...this.getAnimation()}
  