Use querySelector for consistency with rest of codebase

src/plugins/muc-views/modals/muc-list.js

@@ -111,7 +111,7 @@ export default class MUCListModal extends BaseModal {
     }
 
     onDomainChange () {
-        this.getElementsByClassName('form-control')[0].value = this.model.get('muc_domain');
+        this.querySelector('form-control').value = this.model.get('muc_domain');
         this.items = [];
         this.model.save('feedback_text', '');
         api.settings.get('auto_list_rooms') && this.updateRoomsList();