Roll Observatory packages and add a roll script

packages/quiver/lib/src/streams/concat.dart

 // Copyright 2014 Google Inc. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 65 matching lines @@
     }, onCancel: () {
       if (currentSubscription != null) return currentSubscription.cancel();
     });
 
     nextStream();
 
     return controller.stream.listen(onData,
         onError: onError, onDone: onDone, cancelOnError: cancelOnError);
   }
 }