replace downstream core

composer.json

@@ -17,6 +17,9 @@
   ],
   "minimum-stability": "alpha",
   "prefer-stable": true,
+  "replace": {
+    "drupal/core": "*"
+  },
   "require": {
     "composer/installers": "^1.7",
     "oomphinc/composer-installers-extender": "^1.1",