flutter pub upgrade (#178)

isolate_example/lib/data_transfer_page.dart

@@ -23,7 +23,7 @@ class DataTransferPageStarter extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return ChangeNotifierProvider(
-      builder: (context) => DataTransferIsolateController(),
+      create: (context) => DataTransferIsolateController(),
       child: DataTransferPage(),
     );
   }