Use package:sky imports consistently

sky/sdk/lib/widgets/modal_overlay.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 'widget.dart';
+import 'package:sky/widgets/basic.dart';
+import 'package:sky/widgets/widget.dart';
 
 class ModalOverlay extends Component {
 
   ModalOverlay({ String key, this.children, this.onDismiss }) : super(key: key);
 
   final List<Widget> children;
   final Function onDismiss;
 
   Widget build() {
     return new Listener(
       onGestureTap: (_) {
         if (onDismiss != null)
           onDismiss();
       },
       child: new Stack(children)
     );
   }
 
 }