Use package:sky imports consistently

sky/sdk/lib/widgets/menu_divider.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 'basic.dart';
-import 'theme.dart';
+import 'package:sky/widgets/basic.dart';
+import 'package:sky/widgets/theme.dart';
 
 class MenuDivider extends Component {
   MenuDivider({ String key }) : super(key: key);
 
   Widget build() {
     return new Container(
       height: 0.0,
       decoration: new BoxDecoration(
         border: new Border(
           bottom: new BorderSide(
             color: Theme.of(this).dividerColor
           )
         )
       ),
       margin: const EdgeDims.symmetric(vertical: 8.0)
     );
   }
 }