Update FilesSignature.cs

[xiezheng-XD]

做了以下几点改动：
1.使用 Path.Combine() 确保路径的正确性，使其在各系统下均能兼容
2.修复了代码中的一些变量命名和拼写错误
3.对文件处理部分做了优化

[tencent-adm]

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