Fix minor warnings (#673)

experimental/web_dashboard/lib/src/widgets/third_party/adaptive_scaffold.dart

@@ -140,7 +140,7 @@ class _AdaptiveScaffoldState extends State<AdaptiveScaffold> {
           ...widget.destinations.map(
             (d) => BottomNavigationBarItem(
               icon: Icon(d.icon),
-              title: Text(d.title),
+              label: d.title,
             ),
           ),
         ],

navigation_and_routing/lib/nav_1/on_generate_route.dart

@@ -57,7 +57,7 @@ class HomeScreen extends StatelessWidget {
 }
 
 class DetailScreen extends StatelessWidget {
-  String id;
+  final String id;
 
   DetailScreen({
     this.id,