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

lib/components/dropdown.dart

 import 'dart:async';
 import 'dart:html';
 import 'package:bot/bot.dart';
 import 'package:web_ui/web_ui.dart';
 import 'package:widget/effects.dart';
 import 'package:widget/widget.dart';
 
 // TODO: esc and click outside to collapse
 // https://github.com/kevmoo/widget.dart/issues/14
 
@@ skipping 29 matching lines @@
       if(value) {
         // before we set the local shown value, ensure
         // all of the other dropdowns are closed
         closeDropdowns();
       }
 
       _isShown = value;
 
       final action = _isShown ? ShowHideAction.SHOW : ShowHideAction.HIDE;
 
-      final headerElement = this.query('x-dropdown > .dropdown');
+      final headerElement = this.query('[is=x-dropdown] > .dropdown');
 
       if(headerElement != null) {
         if(_isShown) {
           headerElement.classes.add('open');
         } else {
           headerElement.classes.remove('open');
         }
       }
 
-      final contentDiv = this.query('x-dropdown > .dropdown-menu');
+      final contentDiv = this.query('[is=x-dropdown] > .dropdown-menu');
       if(contentDiv != null) {
         ShowHide.begin(action, contentDiv, effect: _effect);
       }
       ShowHideComponent.dispatchToggleEvent(this);
     }
   }
 
   Stream<Event> get onToggle => ShowHideComponent.toggleEvent.forTarget(this);
 
   void hide() {
     isShown = false;
   }
 
   void show() {
     isShown = true;
   }
 
   void toggle() {
     isShown = !isShown;
   }
 
   static void closeDropdowns() {
-    document.queryAll('x-dropdown')
+    document.queryAll('[is=x-dropdown]')
       .where((e) => e.xtag is Dropdown)
       .map((e) => e.xtag as Dropdown)
       .forEach((dd) => dd.hide());
   }
 
   @protected
   void created() {
     this.onClick.listen(_onClick);
     this.onKeyDown.listen(_onKeyDown);
   }
 
   void _onKeyDown(KeyboardEvent e) {
     if(!e.defaultPrevented && e.keyCode == KeyCode.ESC) {
       this.hide();
       e.preventDefault();
     }
   }
 
   void _onClick(MouseEvent event) {
     if(!event.defaultPrevented && event.target is Element) {
       final Element target = event.target;
       if(target != null && target.dataset['toggle'] == 'dropdown') {
         toggle();
         event.preventDefault();
         target.focus();
       }
     }
   }
 }