0.2.4

• remove nonextendable on $plugins and $pluginOrder

as nonextendable will call [Object.preventExtensions`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/preventExtensions) on dispatcher's plugins and order. Which will block dynamic plugin. So I remove it.
If you wish it return, I will try some other method, clone etc.