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

lib/src/effects/modal_manager.dart

 part of effects;
 
 /**
  * [ModalManager] is inspired by the [modal helper](http://twitter.github.com/bootstrap/javascript.html#modals) in Bootstrap.
  *
  * It has two static methods `show` and `hide` that both take the same parameters as corresponding methods in [ShowHide].
  *
  * [ModalManager] controls the display of the provided element while also creating a dark backdrop on the page.
  * Any element used should have a fixed position, a z-index greater than 1040, and an initial display of none.
  */
@@ skipping 22 matching lines @@
 
     final backDropElement = _getBackdrop(element.document, false);
 
     final futures = [ShowHide.hide(element, effect: effect, duration: duration, effectTiming: effectTiming)];
 
     if(backDropElement != null) {
       futures.add(ShowHide.hide(backDropElement, effect: new FadeEffect()));
     }
 
     return Future.wait(futures)
-        .catchError((AsyncError err) {
+        .catchError((err) {
           print(err);
         }, test: (v) => false)
         ..whenComplete(() => _clearOutBackdrop(element.document));
   }
 
   static void _clearOutBackdrop(HtmlDocument doc) {
     final backdrop = _getBackdrop(doc, false);
     if(backdrop != null) {
       backdrop.remove();
     }
   }
 
   static Element _getBackdrop(HtmlDocument parentDocument, bool addIfMissing) {
     assert(parentDocument != null);
 
 
     Element element = parentDocument.body.query('.$_backdropClass');
     if(element == null && addIfMissing) {
       element = new DivElement()
         ..classes.add(_backdropClass)
         ..attributes['style'] = _backdropStyle;
       parentDocument.body.children.add(element);
     }
 
     return element;
   }
 }