Fix GIF Disappear when return from background

Summary:
GIF Image will disappear after press the home button and return back.
Set `removedOnCompletion` to be`false` will fix  all `CAAnimation` disappear like stopping after going into the background.
Closes https://github.com/facebook/react-native/pull/7612

Differential Revision: D3481403

fbshipit-source-id: 101bded300f5e34bb53ec6c54a40eb5aece22fba

Libraries/Image/RCTGIFImageDecoder.m

@@ -91,6 +91,7 @@ RCT_EXPORT_MODULE()
     animation.keyTimes = keyTimes;
     animation.values = images;
     animation.duration = duration;
+    animation.removedOnCompletion = NO;
     image.reactKeyframeAnimation = animation;
 
   } else {