Send message to server.

        data: message to send. If you set opcode to OPCODE_TEXT,
              data must be utf-8 string or unicode.
        opcode: operation code of data. default is OPCODE_TEXT.

def send(self, data, opcode=websocket.ABNF.OPCODE_TEXT):
        """
        Send message to server.

        data: message to send. If you set opcode to OPCODE_TEXT,
              data must be utf-8 string or unicode.
        opcode: operation code of data. default is OPCODE_TEXT.
        """
        self.ws_client.send(data, opcode)