Fix widget.dart to work with the latest web_ui library. Specifically, query selectors need to use "…

lib/components/tabs.dart

 import 'dart:html';
 import 'package:web_ui/web_ui.dart';
 import 'package:bot/bot.dart';
 import 'package:widget/effects.dart';
 import 'package:widget/widget.dart';
 
 // TODO:TEST: no active tabs -> first is active
 // TODO:TEST: 2+ active tabs -> all but first is active
 // TODO:TEST: no tabs -> no crash
 
@@ skipping 74 matching lines @@
     String target = clickedElement.dataset['target'];
     if(target == null) {
       final href = clickedElement.attributes['href'];
       if(href != null && href.startsWith('#')) {
         target = href.substring(1);
       }
     }
     return target;
   }
 
-  List<Element> _getAllTabs() => this.queryAll('x-tabs > .nav-tabs > li');
+  List<Element> _getAllTabs() => this.queryAll('[is=x-tabs] > .nav-tabs > li');
 
   void _ensureAtMostOneTabActive() {
     final tabs = _getAllTabs();
     Element activeTab = null;
     tabs.forEach((Element tab) {
       if(tab.classes.contains('active')) {
         if(activeTab == null) {
           activeTab = tab;
         } else {
           tab.classes.remove('active');
         }
       }
     });
 
     if(activeTab == null && !tabs.isEmpty) {
       activeTab = tabs[0];
       activeTab.classes.add('active');
     }
   }
 
   SwapComponent _getSwap() {
-    final Element element = this.query('x-tabs > x-swap');
+    final Element element = this.query('[is=x-tabs] > [is=x-swap]');
     if(element != null) {
       if(element is SwapComponent) {
         return element;
       } else if(element.xtag is SwapComponent) {
         return element.xtag;
       }
     }
     return null;
   }
 
   void _updateContent(String target) {
     final swap = _getSwap();
 
     if(swap != null) {
       final items = swap.items;
 
       final targetItem = $(items).firstWhere((e) => e.id == target, orElse: () => null);
       if(targetItem != null) {
         swap.showItem(targetItem);
       }
     }
   }
 }