Fix lint issue

lib/src/ui/keyboard_visibility.dart

@@ -36,7 +36,7 @@ class KeyboardVisibiltyState extends State<KeyboardVisibilty>
 
   @override
   void didChangeMetrics() {
-    final bottomInset = window.viewInsets.bottom;
+    final bottomInset = View.of(context).viewInsets.bottom;
 
     if (bottomInset != _lastBottomInset) {
       if (bottomInset > 0) {