Use package:sky imports consistently

sky/sdk/lib/widgets/material.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import '../animation/animation_performance.dart';
-import '../painting/box_painter.dart';
-import 'animated_component.dart';
-import 'animation_builder.dart';
-import 'basic.dart';
-import 'default_text_style.dart';
-import 'theme.dart';
+import 'package:sky/animation/animation_performance.dart';
+import 'package:sky/painting/box_painter.dart';
+import 'package:sky/widgets/animated_component.dart';
+import 'package:sky/widgets/animation_builder.dart';
+import 'package:sky/widgets/basic.dart';
+import 'package:sky/widgets/default_text_style.dart';
+import 'package:sky/widgets/theme.dart';
 
 enum MaterialType { canvas, card, circle, button }
 
 const Map<MaterialType, double> edges = const {
   MaterialType.canvas: null,
   MaterialType.card: 2.0,
   MaterialType.circle: null,
   MaterialType.button: 2.0,
 };
 
@@ skipping 62 matching lines @@
     return color == null ? null : new AnimatedColor(color);
   }
 
   Widget build() {
     return _builder.build(
         new DefaultTextStyle(style: Theme.of(this).text.body1, child: child)
     );
   }
 
 }