dart fix

example/lib/output_device/output_device.dart

@@ -11,16 +11,16 @@ import 'package:logging/logging.dart';
 /// menu to change from all available output devices.
 /// All this is made simple just using the `listPlaybackDevices` and
 /// `changeDevice` methods.
-/// 
+///
 /// To get all output devices use `listPlaybackDevices` which returns
 /// a list of `PlaybackDevice`s class. Each items of this class
 /// contains the id, whether it's the default device (the one used by the OS)
 /// and the name.
 /// This method can be called even if the engine has not been initialized.
-/// 
+///
 /// At any time it is possible to pass to `changeDevice` a `PlaybackDevice`
 /// which will change the output device.
-/// 
+///
 /// Note: Android, iOS and Web, only support one output device which is
 /// the default.
 
@@ -75,7 +75,7 @@ class _HelloFlutterSoLoudState extends State<HelloFlutterSoLoud> {
       currentSound = value;
       SoLoud.instance.play(currentSound!, looping: true, volume: 0.5);
     });
-    
+
     devices = SoLoud.instance.listPlaybackDevices();
     assert(devices.isNotEmpty, 'No devices found!');