Change a port number in the specs to avoid a potential conflict

test/test_serializer.rb

@@ -19,7 +19,7 @@
       begin
         assert_equal JSON, memcache.instance_variable_get('@ring').servers.first.serializer
 
-        memcached(19128) do |newdc|
+        memcached(21956) do |newdc|
           assert newdc.set("json_test", {"foo" => "bar"})
           assert_equal({"foo" => "bar"}, newdc.get("json_test"))
         end