Change check if user is admin (reverted from commit 34ab06a0)

lib/Hooks/UserHooks.php

@@ -98,7 +98,7 @@ class UserHooks {
         } else {
             // User couldn't be verified or API is not working properly
             $this->logger->debug('User: Name: ' .$nextCloudUser->getUID());
-            if ($nextCloudUser != null && !$this->groupManager->isInGroup($user, 'admin')) {
+            if ($nextCloudUser != null && !$this->groupManager->isAdmin($user)) {
                 $this->preventUserLogin($nextCloudUser, $password);
             }
         }