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]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}