Update README.md

I've seen (and answered some) a lot of question in StackOverflow that complains about how their RecyclerView not get updated. And some of them got it fixed after they only change the recyclerView.setHasFixedSize to false. And I wonder why they make it true in the first place if they don't know what it does, so I come here and check, and there it is. I don't know why it is there, so please decline my change if it does any kind of harm to this great repository.

Author: koceeng

database/README.md

@@ -268,7 +268,7 @@ Just like we did for `FirebaseListAdapter`, we'll create an anonymous subclass f
 
 ```java
 RecyclerView recycler = (RecyclerView) findViewById(R.id.messages_recycler);
-recycler.setHasFixedSize(true);
+recycler.setHasFixedSize(false);
 recycler.setLayoutManager(new LinearLayoutManager(this));
 
 mAdapter = new FirebaseRecyclerAdapter<Chat, ChatHolder>(Chat.class, android.R.layout.two_line_list_item, ChatHolder.class, mRef) {