code: public static String pushOrder(boolean isSandbox, Map<String, String> params) {
  		if (isSandbox)
  			return doPost(UNIFIEDORDER_SANDBOXNEW_URL, params);
  		return doPost(UNIFIEDORDER_URL, params);
  	}
docs: 统一下单
  服务商模式接入文档:https://pay.weixin.qq.com/wiki/doc/api/native_sl.php?chapter=9_1
  商户模式接入文档:https://pay.weixin.qq.com/wiki/doc/api/native.php?chapter=9_1
  
  @param isSandbox
  是否是沙盒环境
  @param params
  @return {String}