docs: Update README.md

Author: markusrubey

README.md

@@ -20,7 +20,7 @@ dependencies:
   nstack:
     git:
       url: git://github.com/nstack-io/flutter-sdk.git
-      ref: v0.4.0
+      ref: v0.4.1
 
 dev_dependencies:
   build_runner:
@@ -98,4 +98,4 @@ class MyApp extends StatelessWidget {
 
 [build_runner]: https://pub.dev/packages/build_runner
 [NStack]: https://nstack.io
-[AppOpen]: https://nstack-io.github.io/docs/docs/app-open.html
+[AppOpen]: https://nstack-io.github.io/docs/docs/app-open.html