renderer: use composition api as default

src/renderer/components/screen/ErrorScreen.vue

@@ -6,6 +6,8 @@
 
 <script>
 export default {
-  name: 'ErrorScreen'
+  setup () {
+
+  }
 }
 </script>

src/renderer/components/screen/MainScreen.vue

@@ -1,11 +1,19 @@
 <template>
   <div>
-    Main Screen
+    Main Screen {{ test }}
   </div>
 </template>
 
 <script>
+import { ref } from 'vue'
+
 export default {
-  name: 'MainScreen'
+  setup () {
+    const test = ref(1)
+
+    return {
+      test
+    }
+  }
 }
 </script>