Change healthcheck url to /wp-includes/version.php

Per @murgero's suggestion at https://forum.cloudron.io/topic/1733/hiding-wordpress-app-login-page-create-backup-problem/12

CloudronManifest.json

@@ -5,7 +5,7 @@
   "description": "file://DESCRIPTION.md",
   "tagline": "Transform your site into almost anything",
   "version": "2.5.0-1",
-  "healthCheckPath": "/wp-login.php",
+  "healthCheckPath": "/wp-includes/version.php",
   "httpPort": 8000,
   "manifestVersion": 1,
   "website": "https://wordpress.org/",