[bug report] the zip file generated after downloading the element UI theme on the official website is decompressed and an error is reported

### Element UI version
2.15.0

### OS/Browsers version
win10专业版 / 谷歌浏览器 88.0.4324.146

### Vue version
2.6.12

### Reproduction Link
https://codepen.io/ziyoung/pen/xxx

### Steps to reproduce
1、进入主题预览页面：http://element.eleme.cn/#/zh-CN/theme
2、进入主题对应主题
3、下载主题

### What is Expected?
成功解压zip包

### What is actually happening?
解压zip包失败