Minor change: php marker lowercase for code highlight in gitlab.

README.md

@@ -21,7 +21,7 @@ See: https://www.drupal.org/node/895232 for further information.
 There is no UI. The configuration is only possible via settings.php to keep it very lightweight because of the [Middleware situation](https://www.drupal.org/docs/8/api/middleware-api/overview). Keep sure that all host you would give access are not protected via core trusted_hosts setting.
 
 ### Example config:
-```PHP
+```php
 $settings['firewall']['enabled'] = TRUE;
 $settings['firewall']['bypass']['hosts'] = ['admin.example.com'];
 $settings['firewall']['bypass']['client_ips'] = ['127.0.0.1'];