Fix incorrect GIF message bubble sizing (#1300)

TSAnimatedAdapter is used when rendering GIFs. TSAnimatedAdapter
inherits from JSQMediaItem but does not provide a custom implementation
of the hash method. The default implementation of hash in JSQMediaItem
results in all messages of a given interaction type (incoming,
outgoing) sharing a cached bubble size. For this reason, JSQMediaItem
subclasses are required to implement hash (see
https://github.com/jessesquires/JSQMessagesViewController/issues/631).

This commit fixes issue #1275 by implementing hash in TSAnimatedAdapter
the same way TSPhotoAdapter does.

Signal/src/Models/TSMessageAdapaters/TSAnimatedAdapter.m

@@ -56,6 +56,13 @@
     _cachedImageView = nil;
 }
 
+#pragma mark - NSObject
+
+- (NSUInteger)hash
+{
+    return super.hash ^ self.image.hash;
+}
+
 #pragma mark - JSQMessageMediaData protocol
 
 - (UIView *)mediaView {