Update charted to 0.4.8 and roll

packages/charted/lib/charts/data_transformers/transpose_transformer.dart

 //
 // Copyright 2014 Google Inc. All rights reserved.
 //
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file or at
 // https://developers.google.com/open-source/licenses/bsd
 //
 
 part of charted.charts;
 
 /// Transforms the ChartData by transposing the columns and rows.  A label column
 /// index in the original data will need to be specified (default to 0), all
 /// values in the specified label column will be used as the label for the
 /// transformed data, all the labels in the original Chart data columns will be
 /// populated in the label column as values of that column.
 ///
 /// All values in the data except for the data in the label column must have the
 /// same type; All columns except for the label column must have the same
 /// formatter if a formatter exist for columns.
-class TransposeTransformer extends ChangeNotifier
+class TransposeTransformer extends Observable
     implements ChartDataTransform, ChartData {
   final SubscriptionsDisposer _dataSubscriptions = new SubscriptionsDisposer();
   ObservableList<ChartColumnSpec> columns = new ObservableList();
   ObservableList<List> rows = new ObservableList();
 
   // If specified, this values of this column in the input chart data will be
   // used as labels of the transposed column label.  Defaults to first column.
   int _labelColumn;
   ChartData _data;
 
@@ skipping 80 matching lines @@
       columns.add(
           new ChartColumnSpec(type: type, label: label, formatter: formatter));
     }
     columns.insert(
         _labelColumn,
         new ChartColumnSpec(
             type: ChartColumnSpec.TYPE_STRING,
             label: _data.columns.elementAt(_labelColumn).label));
   }
 }