Roll Observatory packages and add a roll script

packages/quiver/lib/streams.dart

 // Copyright 2013 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,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
 library quiver.streams;
 
 import 'dart:async';
 import 'package:quiver/iterables.dart' show IndexedValue;
 
 part 'src/streams/collect.dart';
 part 'src/streams/concat.dart';
 part 'src/streams/enumerate.dart';
 part 'src/streams/streambuffer.dart';