Added group toJSON conversion and fixed syntax errors

test/helpers/api-integration/api-classes.js

@@ -80,9 +80,7 @@ export class ApiGroup extends ApiObject {
 
     let update = { chat };
 
-    this.update(update, '$push');
-
-    return this;
+    return await this.update(update);
   }
 }
 

website/src/controllers/api-v3/groups.js

@@ -153,6 +153,7 @@ api.getGroup = {
     if (!group) throw new NotFound(res.t('groupNotFound'));
 
     if (!user.contributor.admin) {
+      group = group.toJSON();
       _.remove(group.chat, function removeChat (chat) {
         chat.flags = {};
         return chat.flagCount >= 2;