fix latest pedantic lints (#107)

Author: kevmoo

lib/dom.dart

@@ -830,8 +830,7 @@ class FilteredElementList extends IterableBase<Element>
   //
   // TODO(nweiz): we don't always need to create a new list. For example
   // forEach, every, any, ... could directly work on the _childNodes.
-  List<Element> get _filtered =>
-      List<Element>.from(_childNodes.where((n) => n is Element));
+  List<Element> get _filtered => _childNodes.whereType<Element>().toList();
 
   void forEach(void f(Element element)) {
     _filtered.forEach(f);

test/support.dart

@@ -26,7 +26,7 @@ final testDataDir = p.join(testDir, 'data');
 
 Iterable<String> getDataFiles(String subdirectory) {
   var dir = Directory(p.join(testDataDir, subdirectory));
-  return dir.listSync().where((f) => f is File).map((f) => f.path);
+  return dir.listSync().whereType<File>().map((f) => f.path);
 }
 
 // TODO(jmesserly): make this class simpler. We could probably split on