refactor: require Node 8

BREAKING CHANGE: @vue/cli-service and all plugins now require Node version 8+.

Author: yyx990803

.eslintrc

@@ -4,7 +4,6 @@
     "jest": true
   },
   "rules": {
-    "indent": ["error", 2, { "MemberExpression": "off" }],
-    "vue-libs/no-async-functions": 2
+    "indent": ["error", 2, { "MemberExpression": "off" }]
   }
 }

packages/@vue/cli-plugin-e2e-cypress/__tests__/.eslintrc

@@ -2,8 +2,8 @@ const defaults = {
   name: 'PWA app',
   themeColor: '#4DBA87', // The Vue color
   msTileColor: '#000000',
-  appleMobileWebAppCapable: "no",
-  appleMobileWebAppStatusBarStyle: "default",
+  appleMobileWebAppCapable: 'no',
+  appleMobileWebAppStatusBarStyle: 'default'
 }
 
 module.exports = class HtmlPwaPlugin {

packages/@vue/cli-plugin-e2e-nightwatch/__tests__/.eslintrc

@@ -74,6 +74,6 @@
     "access": "public"
   },
   "engines": {
-    "node": ">=6"
+    "node": ">=8"
   }
 }