script: Update rust-selectors to get :active support.

I couldn't find the place in the spec where the precise behavior of
`:active` is described, so I don't set it. However, all the machinery to
keep track of its status is in place.

Improves YouTube.

components/layout/wrapper.rs

@@ -478,6 +478,12 @@ impl<'le> ::selectors::Element for LayoutElement<'le> {
         node.get_focus_state_for_layout()
     }
 
+    #[inline]
+    fn get_active_state(&self) -> bool {
+        let node = NodeCast::from_layout_js(&self.element);
+        node.get_active_state_for_layout()
+    }
+
     #[inline]
     fn get_id(&self) -> Option<Atom> {
         unsafe {