[Bug Report] Theme builder - download function causes request timeout error

### Element UI version
2.15.7

### OS/Browsers version
Chrome v 97.0.4692.71

### Vue version
2.6.14

### Reproduction Link
https://github.com/wedbew/element

### Steps to reproduce
1. Go to https://element.eleme.io/#/en-US/theme
2. Define color schema, you can basically change nothing
3. Click on download button
4. Then alert with Request Timeout appear.

### What is Expected?
To download the theme variables

### What is actually happening?
Request timeout, on mounted lifecycle hook -
e.onerror = function (t) {
ga('send', 'event', 'DocView', 'Ali', 'Outer'),
console.error(t)
},