Fix missing keys in animation example

Summary:
There were two warnings about missing keys, fixed them.
Closes https://github.com/facebook/react-native/pull/5153

Reviewed By: svcscm

Differential Revision: D2807602

Pulled By: androidtrunkagent

fb-gh-sync-id: ef7a5eecd297e89b7338fdec65639785a1232f13

Examples/UIExplorer/AnimatedGratuitousApp/AnExBobble.js

@@ -95,6 +95,7 @@ class AnExBobble extends React.Component {
           return (
             <Animated.Image
               {...handlers}
+              key={i}
               source={{uri: BOBBLE_IMGS[j]}}
               style={[styles.circle, {
                 backgroundColor: randColor(),                             // re-renders are obvious

Examples/UIExplorer/AnimatedGratuitousApp/AnExChained.js

@@ -77,6 +77,7 @@ class AnExChained extends React.Component {
           return (
             <Animated.Image
               {...handlers}
+              key={i}
               source={{uri: CHAIN_IMGS[j]}}
               style={[styles.sticker, {
                 transform: this.state.stickers[j].getTranslateTransform(), // simple conversion