Update charted to 0.4.8 and roll

packages/charted/lib/charts/chart_data.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;
 
 ///
 /// Interface to be implemented by data providers to give tabular access to
 /// data for chart renderers.
 ///
 abstract class ChartData {
   /// Read-only access to column specs
   Iterable<ChartColumnSpec> get columns;
 
   /// Read-only access to rows
   Iterable<List> get rows;
 
   /// Create a new instance of [ChartData]'s internal implementation
   factory ChartData(Iterable<ChartColumnSpec> columns,
-      Iterable<Iterable> rows) = DefaultChartDataImpl;
+      List<List> rows) = DefaultChartDataImpl;
 }
 
 ///
 /// Interface implemented by [ChartData] transformers.
 /// Examples:
 ///   [AggregationTransformer] to compute aggregated rows/columns
 ///   [FilterTransformer] to filter data
 ///   [TransposeTransformer] to convert rows to columns and vice-versa
 ///
 abstract class ChartDataTransform {
@@ skipping 76 matching lines @@
 
   ChartColumnSpec(
       {this.label,
       String type: TYPE_NUMBER,
       this.formatter,
       bool useOrdinalScale})
       : useOrdinalScale = useOrdinalScale == true ||
             useOrdinalScale == null && ORDINAL_SCALES.contains(type),
         type = type;
 }