pkg/js: update version, example, and SDK constraint for annotation change

pkg/js/example/chart.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library chart;
 
 import 'dart:html';
 import 'package:js/js.dart';
 
-@Js()
+@JS()
 class Chart {
   external Chart(CanvasRenderingContext2D ctx);
 
   external dynamic Line(Data data, Options options);
 }
 
-@Js()
+@JS()
 class Data {
   external List get labels;
   external List<DataSet> get datasets;
 
   external factory Data({List<String> labels, List<DataSet> datasets});
 }
 
 /// Minimal implementation of dataset for line chart
 ///
 /// http://www.chartjs.org/docs/#line-chart-data-structure
-@Js()
+@JS()
 class DataSet {
   external String get label;
   external String get fillColor;
   external String get strokeColor;
   external String get pointColor;
   external String get pointStrokeColor;
   external String get pointHighlightFill;
   external String get pointHighlightStroke;
 
   external List<num> get data;
 
   external factory DataSet(
       {String label,
       String fillColor,
       String strokeColor,
       String pointColor,
       String pointStrokeColor,
       String pointHighlightFill,
       String pointHighlightStroke,
       List<num> data});
 }
 
 /// Minimal implementation of options
 ///
 /// http://www.chartjs.org/docs/#getting-started-global-chart-configuration
-@Js()
+@JS()
 class Options {
   external bool get responsive;
 
   external factory Options({bool responsive});
 }