doc/dart: minor fix to example code

doc/languages-frameworks/dart.section.md

@@ -101,7 +101,7 @@ See the [Dart documentation](#ssec-dart-applications) for more details on requir
 `flutter` in Nixpkgs always points to `flutterPackages.stable`, which is the latest packaged version. To avoid unforeseen breakage during upgrade, packages in Nixpkgs should use a specific flutter version, such as `flutter319` and `flutter322`, instead of using `flutter` directly.
 
 ```nix
-{ flutter, fetchFromGitHub }:
+{ flutter322, fetchFromGitHub }:
 
 flutter322.buildFlutterApplication {
  pname = "firmware-updater";