Roll Observatory packages and add a roll script

quiver/lib/src/iterables/concat.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.
-
-part of quiver.iterables;
-
-/**
- * Returns the concatentation of the input iterables.
- *
- * The returned iterable is a lazily-evaluated view on the input iterables.
- */
-Iterable concat(Iterable<Iterable> iterables) => iterables.expand((x) => x);