Fix group token updates being sent to all clients

src/resolvers/group.resolver.ts

@@ -27,7 +27,7 @@ export class GroupResolver {
 
     @Subscription(() => Group, {
         filter: (payload, variables) =>
-            payload.updateToken.code === variables.groupCode,
+            payload.updateToken.slug === variables.groupSlug,
     })
     async updateToken(
         @Args({ name: 'groupSlug', type: () => GraphQLString })