[Bug Report] win7无法访问官网

### Element UI version
2.15.9

### OS/Browsers version
win7

### Vue version
2.7.10

### Reproduction Link
https://elementui.github.io/

### Steps to reproduce
win7打开官网白屏报错 https://element.eleme.io/#/zh-CN
Failed to load resource: net::ERR_CONNECTION_RESET
vue.runtime.min.js:1 Failed to load resource: net::ERR_CONNECTION_RESET
vue-router.min.js:1 Failed to load resource: net::ERR_CONNECTION_RESET
highlight.pack.b1f71b31-3c07-11e9-ba1a-55bba1877129.js:1 Failed to load resource: net::ERR_CONNECTION_RESET
docs.586f45c.js:1 Uncaught ReferenceError: Vue is not defined
at Object. (docs.586f45c.js:1:11063)
at B (docs.586f45c.js:1:6870)
at r (docs.586f45c.js:1:7169)
at Module. (docs.586f45c.js:1:115187)
at Module. (docs.586f45c.js:1:116287)
at B (docs.586f45c.js:1:6870)
at c (docs.586f45c.js:1:387)
at docs.586f45c.js:1:10253
at docs.586f45c.js:1:10257

### What is Expected?
希望win7可以访问官网

### What is actually happening?
希望win7可以访问官网