Modify handling of @code.

First of all, I would like to say thank you for your great work!

17469d9a5986dd9cd8d5f9d07b27e9d0d3b2f23b seems to corrupt handling of @code in `handler05.rb`.

For example, the following does not work well:
```ruby
# 'code' is ignored.
frame = WebSocket::Frame::Outgoing::Client.new(type: :close, code: 1000, version: 13)
```

This is just a simple patch, so please modify in more appropriate way if this patch is not so good.