Fix deprecated v-content (#1410)

Author: DimNS

client-generator/vuetify.md

@@ -210,10 +210,10 @@ Update your App.vue:
       <v-toolbar-title>Application</v-toolbar-title>
     </v-app-bar>
 
-    <v-content>
+    <v-main>
       <Breadcrumb layout-class="pl-3 py-3" />
       <router-view></router-view>
-    </v-content>
+    </v-main>
     <v-footer color="indigo" app>
       <span class="white--text">&copy; 2019</span>
     </v-footer>