renderer: use export default at once

src/renderer/plugins/vuetify.js

@@ -1,9 +1,7 @@
 import { createVuetify } from 'vuetify/dist/vuetify'
 
-const vuetify = createVuetify({
+export default createVuetify({
   icons: {
     iconfont: 'mdi'
   }
 })
-
-export default vuetify

src/renderer/router/index.js

@@ -1,7 +1,7 @@
 import { createRouter, createWebHashHistory } from 'vue-router/dist/vue-router.esm-bundler'
 import { MainScreen, ErrorScreen } from '../components/screen'
 
-const router = createRouter({
+export default createRouter({
   history: createWebHashHistory(),
   routes: [
     {
@@ -18,5 +18,3 @@ const router = createRouter({
     }
   ]
 })
-
-export default router