Allow johnpbloch/wordpress-core-installer to write (#117)

Author: danielbachhuber

composer.json

@@ -24,7 +24,8 @@
         "process-timeout": 7200,
         "sort-packages": true,
         "allow-plugins": {
-            "dealerdirect/phpcodesniffer-composer-installer": true
+            "dealerdirect/phpcodesniffer-composer-installer": true,
+            "johnpbloch/wordpress-core-installer": true
         }
     },
     "extra": {