WxPayKit#appPrepayIdCreateSign 方法中Map Key错误

### 版本信息
- IJPay 版本: 2.1.1-2.2.0
- 支付方式:微信APP支付

### 相关代码

原代码
```java
packageParams.put("appId", appId);
packageParams.put("partnerid", partnerId);
packageParams.put("prepayid", prepayId);
packageParams.put("package", "Sign=WXPay");
packageParams.put("nonceStr", String.valueOf(System.currentTimeMillis()));
packageParams.put("timeStamp", String.valueOf(System.currentTimeMillis() / 1000));
if (signType == null) {
    signType = SignType.MD5;
}
packageParams.put("signType", signType.getType());
String packageSign = WxPayKit.createSign(packageParams, partnerKey, signType);
```

正确代码
```java
packageParams.put("appid", appId);
packageParams.put("partnerid", partnerId);
packageParams.put("prepayid", prepayId);
packageParams.put("package", "Sign=WXPay");
packageParams.put("noncestr", String.valueOf(System.currentTimeMillis()));
packageParams.put("timestamp", String.valueOf(System.currentTimeMillis() / 1000));
if (signType == null) {
    signType = SignType.MD5;
}
String packageSign = WxPayKit.createSign(packageParams, partnerKey, signType);
packageParams.put("signType", signType.getType());
```

#### 相关文档

[APP支付 业务流程](https://pay.weixin.qq.com/wiki/doc/api/app/app.php?chapter=8_3)

> 步骤3：统一下单接口返回正常的prepay_id，再按签名规范重新生成签名后，将数据传输给APP。参与签名的字段名为appid，partnerid，prepayid，noncestr，timestamp，package。注意：package的值格式为Sign=WXPay

GVP Javen/IJPay

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GVPJaven/IJPay

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