Advance html5lib to newest breaking changes in core: getKeys -> keys, etc

lib/src/list_proxy.dart

Index: lib/src/list_proxy.dart
diff --git a/lib/src/list_proxy.dart b/lib/src/list_proxy.dart
index 14e3cfe8d743dc27718d720c09d02c189e65b864..4fe32e34c8123c52dfca2d861f027fee3adc7042 100644
--- a/lib/src/list_proxy.dart
+++ b/lib/src/list_proxy.dart
@@ -51,7 +51,7 @@ class ListProxy<E> implements List<E> {
   bool every(bool f(E element)) => _list.every(f);
   bool some(bool f(E element)) => _list.some(f);
   bool get isEmpty => _list.isEmpty;
-  E last() => _list.last();
+  E get last => _list.last;
 
   set length(int value) { _list.length = value; }
   operator []=(int index, E value) { _list[index] = value; }