Update to version of flutter_soloud that’s guaranteed to work

This is after fix alnitak/flutter_soloud#139

Author: filiph

audio_soloud/codelab_rebuild.yaml

@@ -18,7 +18,7 @@ steps:
              flutter:
                sdk: flutter
 
-          +  flutter_soloud: ^2.0.0
+          +  flutter_soloud: ^2.1.6
           +  logging: ^1.2.0
           +
            dev_dependencies: