fixing popsu.theme bug

web/profiles/d8-starterkit-profile

@@ -1 +1 @@
-Subproject commit 5069345d9dffca8ff935d7a01d2bc97a1272f063
+Subproject commit 179aa994156fa9c986cf9eb9262872abb9c651a2

web/themes/custom/popsu/popsu.theme

@@ -69,7 +69,7 @@ function popsu_preprocess_field(&$variables){
       foreach ($element["#items"]->getIterator() as $id => $item) {
         $nid = $item->getValue()['target_id'];
         $variables['items'][$id]['attributes']['class'] = new Attribute();
-        $variables['items'][$id]['attributes']->addClass("programme-".$nid);
+        $variables['items'][$id]['attributes']['class']->addClass("programme-".$nid);
       }
     }
   }