message: Faded scenes in and out to move zoom visible
diff: import React from 'react';
  import {View} from 'react-native';
  +import spring from './spring';
  import NavigationMotion from './NavigationMotion';
  import ZoomMotion from './ZoomMotion';
  export default ({stateNavigator}) => (
  <NavigationMotion
  startStateKey="grid"
  - unmountedStyle={{}}
  - mountedStyle={{}}
  - crumbStyle={{}}
  + unmountedStyle={{opacity: spring(0)}}
  + mountedStyle={{opacity: spring(1)}}
  + crumbStyle={{opacity: spring(0)}}
  style={{flex: 1}}
  stateNavigator={stateNavigator}>
  - {(style, scene, url) => (
  + {({opacity}, scene, url) => (
  <View key={url}
  style={{
  position: 'absolute',
  @@ -20,7 +21,9 @@ export default ({stateNavigator}) => (
  top: 0,
  bottom: 0,
  }}>
  + <View style={{opacity: opacity, flex: 1}}>
  {scene}
  + </View>
  <ZoomMotion stateNavigator={stateNavigator} />
  </View>
  )}
  