code: public OkCoinTradeResult trade(String symbol, String type, String price, String amount)
        throws IOException {
      OkCoinTradeResult tradeResult =
          okCoin.trade(apikey, symbol, type, price, amount, signatureCreator());
      return returnOrThrow(tradeResult);
    }
docs: 下单交易
  
  @param symbol
  @param type
  @param price
  @param amount (只能是整数)
  @return
  @throws IOException