Make RNTester GIF example locate local file system image (#23689)

Summary:
The reason I change GIF image url is `tumblr` blocked in some countries, like China , Kazakhstan, Pakistan, Indonesia. (PS. I can only confirm China blocked it 😂 ), so can we change this to local image?

[iOS] [Fixed] - Make RNTester GIF example locate local file system image
Pull Request resolved: https://github.com/facebook/react-native/pull/23689

Differential Revision: D14275149

Pulled By: cpojer

fbshipit-source-id: c4141cdda40792e5d8bfa805ccc74279e2eef55a

RNTester/js/ImageExample.js

@@ -836,10 +836,7 @@ exports.examples = [
       return (
         <Image
           style={styles.gif}
-          source={{
-            uri:
-              'https://38.media.tumblr.com/9e9bd08c6e2d10561dd1fb4197df4c4e/tumblr_mfqekpMktw1rn90umo1_500.gif',
-          }}
+          source={require('./tumblr_mfqekpMktw1rn90umo1_500.gif')}
         />
       );
     },