Allow wordpress-core-installer in composer.json (#162)

Author: danielbachhuber

composer.json

@@ -27,7 +27,8 @@
     },
     "config": {
         "allow-plugins": {
-            "dealerdirect/phpcodesniffer-composer-installer": true
+            "dealerdirect/phpcodesniffer-composer-installer": true,
+            "johnpbloch/wordpress-core-installer": true
         },
         "sort-packages": true
     },