Roll Observatory packages and add a roll script

packages/observe/lib/src/observer_transform.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.
 
 library observe.src.observer_transform;
 
 import 'package:observe/observe.dart';
 
 /// ObserverTransform is used to dynamically transform observed value(s).
 ///
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   set value(newValue) {
     if (_setTransformer != null) {
       newValue = _setTransformer(newValue);
     }
     _bindable.value = newValue;
   }
 
   deliver() => _bindable.deliver();
 }