change merge to merge!

activesupport/lib/active_support/callbacks.rb

@@ -315,7 +315,7 @@ def initialize(name, config)
         @config = {
           :terminator => "false",
           :scope => [ :kind ]
-        }.merge(config)
+        }.merge!(config)
       end
 
       def compile

activesupport/lib/active_support/hash_with_indifferent_access.rb

@@ -78,7 +78,7 @@ def self.new_from_hash_copying_default(hash)
     end
 
     def self.[](*args)
-      new.merge(Hash[*args])
+      new.merge!(Hash[*args])
     end
 
     alias_method :regular_writer, :[]= unless method_defined?(:regular_writer)