Use package:sky imports consistently

sky/sdk/lib/widgets/dialog.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 '../theme/colors.dart' as colors;
-import 'basic.dart';
-import 'default_text_style.dart';
-import 'material.dart';
-import 'scrollable_viewport.dart';
-import 'theme.dart';
+import 'package:sky/theme/colors.dart' as colors;
+import 'package:sky/widgets/basic.dart';
+import 'package:sky/widgets/default_text_style.dart';
+import 'package:sky/widgets/material.dart';
+import 'package:sky/widgets/scrollable_viewport.dart';
+import 'package:sky/widgets/theme.dart';
 
 /// A material design dialog
 ///
 /// <https://www.google.com/design/spec/components/dialogs.html>
 class Dialog extends Component {
   Dialog({
     String key,
     this.title,
     this.content,
     this.actions,
@@ skipping 70 matching lines @@
               child: new ShrinkWrapWidth(
                 child: new ScrollableBlock(children)
               )
             )
           )
         )
       )
     ]);
   }
 }