Fixed off by one error in packet size, and datatype of keep_alive

Keep Alive packed send from the server
`b'\x06\x00\x00\xc5\xf6\xf3\t'`
Keep Alive packet sent back to server
`b'\x05\x00\x00\xc5\xf6\xf3\t'`

This would cause the minecraft server to drop the client because it failed to decode the packet