Replace example config of drop_chat_states with queue_* in mod_client_state (#1985)

config/ejabberd.exs

@@ -84,7 +84,7 @@ defmodule Ejabberd.ConfigFile do
 
   module :mod_client_state do
     @opts [
-      drop_chat_states: true,
+      queue_chat_states: true,
       queue_presence: false]
   end
 

config/ejabberd.yml

@@ -560,7 +560,7 @@ modules:
   mod_caps: {}
   mod_carboncopy: {}
   mod_client_state:
-    drop_chat_states: true
+    queue_chat_states: true
     queue_presence: false
   mod_configure: {} # requires mod_adhoc
   mod_disco: {}