[node] Also Update::Classes when setting a paint property

Otherwise it has no effect. Tests might be working because a
Update::Classes is also scheduled when adding a new layer.

platform/node/src/node_map.cpp

@@ -598,7 +598,7 @@ NAN_METHOD(NodeMap::SetPaintProperty) {
         return Nan::ThrowTypeError(error->message);
     }
 
-    nodeMap->map->update(mbgl::Update::RecalculateStyle);
+    nodeMap->map->update(mbgl::Update::RecalculateStyle | mbgl::Update::Classes);
     info.GetReturnValue().SetUndefined();
 }