Update charted to 0.4.8 and roll

packages/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);
+/// Returns the concatentation of the input iterables.
+///
+/// The returned iterable is a lazily-evaluated view on the input iterables.
+Iterable<T>
+    concat<T>(Iterable<Iterable<T>> iterables) => iterables.expand((x) => x);