1.下载依赖（官方文档：https://www.npmjs.com/package/vue-cookies）
npm install -g vue-cookies
2.在main.js引入依赖
import Vue from 'vue'
import App from './App'
import router from './router'
import VueCookies from 'vue-cookies'
Vue.use(VueCookies)
3.操作Cookie
3.1写Cookie
this.$cookies.set(keyName, value[, expireTimes[, path[, domain[, secure[, sameSite]]]]]) //return this
3.2读Cookie
this.$cookies.get(keyName) // return value
3.3移除Cookie
this.$cookies.remove(keyName [, path [, domain]]) // return this
3.4判断一个Cookie是否存在
this.$cookies.isKey(keyName) // return false or true
3.5获取所有Cookie的key
this.$cookies.keys() // return a array
