[html5lib] triple slash comment style

pkg/third_party/html5lib/test/dom_test.dart

-/** Additional feature tests that aren't based on test data. */
+/// Additional feature tests that aren't based on test data.
 library dom_test;
 
 import 'package:unittest/unittest.dart';
 import 'package:html5lib/parser.dart';
 
 main() {
   group('Node.querySelector type selectors', () {
     test('x-foo', () {
       expect(parse('<x-foo>').body.querySelector('x-foo'), isNotNull);
     });
@@ skipping 12 matching lines @@
       var doc = parse('<123>');
       expect(() => doc.body.querySelector('123'), throwsUnimplementedError);
     });
 
     test('x\\ny - not implemented', () {
       var doc = parse('<x\\ny>');
       expect(() => doc.body.querySelector('x\\ny'), throwsUnimplementedError);
     });
   });
 }