allow plugin for phpcs

Author: thijskh

composer.json

@@ -12,7 +12,8 @@
         },
         "allow-plugins": {
             "composer/package-versions-deprecated": true,
-            "simplesamlphp/composer-module-installer": true
+            "simplesamlphp/composer-module-installer": true,
+            "dealerdirect/phpcodesniffer-composer-installer": true
         }
     },
     "autoload": {