update license info (#93)

* update license

* update license info in example

Author: prateekmedia

example/lib/home_page.dart

@@ -136,7 +136,7 @@ class _MyHomePageState extends State<MyHomePage> {
                     ],
                     copyright: 'Copyright 2021-2022 Gtk-Flutter Developers',
                     license: const Text(
-                      'GNU LGPL-3.0, This program comes with no warranty.',
+                      'MPL-2.0, This program comes with no warranty.',
                     ),
                   ),
                 ),

lib/src/widgets/adw/switch.dart

@@ -1,5 +1,4 @@
 // Copyright 2014 The Flutter Authors => BSD-3 License
-// Copyright 2022 Gtk-Flutter Authors => LGPL-3 License
 
 import 'dart:ui' show lerpDouble;