Allow composer plugin

Author: swissspidy

composer.json

@@ -46,7 +46,8 @@
   "config": {
     "allow-plugins": {
       "dealerdirect/phpcodesniffer-composer-installer": true,
-      "johnpbloch/wordpress-core-installer": true
+      "johnpbloch/wordpress-core-installer": true,
+      "phpstan/extension-installer": true
     },
     "autoloader-suffix": "WpCliBundle",
     "platform": {