package:observe fix various api issues

pkg/observe/lib/src/metadata.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of observe;
 
 /**
  * Use `@observable` to make a field automatically observable, or to indicate
  * that a property is observable.
  */
@@ skipping 21 matching lines @@
  * observe package. This is necessary to make the member visible to
  * [PathObserver], or similar systems, once the code is deployed.
  */
 const Reflectable reflectable = const Reflectable();
 
 /**
  * An annotation that is used to make a type or member reflectable. This makes
  * it available to [PathObserver] at runtime. For example:
  *
  *     @reflectable
- *     class Monster extends ChangeNotifierBase {
+ *     class Monster extends ChangeNotifier {
  *       int _health;
  *       int get health => _health;
  *       ...
  *     }
  *     ...
  *       // This will work even if the code has been tree-shaken/minified:
  *       final monster = new Monster();
  *       new PathObserver(monster, 'health').changes.listen(...);
  */
 class Reflectable {
   const Reflectable();
 }