Update charted to 0.4.8 and roll

packages/barback/lib/src/utils/cancelable_future.dart

Index: packages/barback/lib/src/utils/cancelable_future.dart
diff --git a/packages/barback/lib/src/utils/cancelable_future.dart b/packages/barback/lib/src/utils/cancelable_future.dart
index 64d2b5fa203e4eb9c98a7039a504325adfb7ccbc..aaa5e3651fca3c283e8c422b8c98418f932090a9 100644
--- a/packages/barback/lib/src/utils/cancelable_future.dart
+++ b/packages/barback/lib/src/utils/cancelable_future.dart
@@ -27,13 +27,15 @@ class CancelableFuture<T> implements Future<T> {
   }
 
   Stream<T> asStream() => _completer.future.asStream();
-  Future catchError(Function onError, {bool test(error)}) =>
-    _completer.future.catchError(onError, test: test);
-  Future then(onValue(T value), {Function onError}) =>
-    _completer.future.then(onValue, onError: onError);
+  Future<T> catchError(Function onError, {bool test(Object error)}) =>
+      _completer.future.catchError(onError, test: test);
+  Future/*<S>*/ then/*<S>*/(/*=FutureOr<S>*/ onValue(T value),
+          {Function onError}) =>
+      _completer.future.then(onValue, onError: onError);
   Future<T> whenComplete(action()) => _completer.future.whenComplete(action);
-  Future timeout(Duration timeLimit, {void onTimeout()}) =>
-    _completer.future.timeout(timeLimit, onTimeout: onTimeout);
+  Future<T> timeout(Duration timeLimit, {void onTimeout()}) =>
+      _completer.future.timeout(timeLimit, onTimeout: onTimeout);
+
   /// Cancels this future.
   void cancel() {
     _canceled = true;