update image on gratuitous example

Summary:
Update image since previous one was deleted

*Test plan (required)**

UIExplorer

<img width="305" alt="screen shot 2017-02-10 at 13 23 11" src="https://cloud.githubusercontent.com/assets/1488195/22821355/1d98dc06-ef94-11e6-8f6b-8e3ea2c328ae.png">
Closes https://github.com/facebook/react-native/pull/12328

Differential Revision: D4550913

fbshipit-source-id: 7a75e80f207394cafbe94402685753e9228442c3

Examples/UIExplorer/js/AnimatedGratuitousApp/AnExTilt.js

@@ -123,7 +123,7 @@ class AnExTilt extends React.Component {
               },
             ],
           }}
-          source={NATURE_IMAGE}
+          source={require('./trees.jpg')}
         />
       </Animated.View>
     );
@@ -142,6 +142,4 @@ var styles = StyleSheet.create({
   },
 });
 
-var NATURE_IMAGE = {uri: 'http://www.deshow.net/d/file/travel/2009-04/scenic-beauty-of-nature-photography-2-504-4.jpg'};
-
 module.exports = AnExTilt;