update undo package

packages/undo/lib/src/change.dart

@@ -0,0 +1,23 @@
+class Change<T> {
+  Change(
+    this._oldValue,
+    this._execute(),
+    this._undo(T oldValue), {
+    this.description = '',
+  });
+
+  final String description;
+
+  final void Function() _execute;
+  final T _oldValue;
+
+  final void Function(T oldValue) _undo;
+
+  void execute() {
+    _execute();
+  }
+
+  void undo() {
+    _undo(_oldValue);
+  }
+}