Can't parse open order websocket messages

[ronkeiser]

Thank you very much for your work on this library.

I'm currently getting a "Can't parse data" error when receiving incoming websocket messages regarding open orders (listening for DataUpdates from AuthClient.SubscribeOpenOrders).

I believe the type assertion data.([]interface{}) is failing. I'm not sure if Kraken changed the message format recently?

[aopoltorzhicky]

Thank you for issue! I fixed it in new release. You can found commit here