Configure composer-drupal-optimization so that it works even if drupal/core is...

Configure composer-drupal-optimization so that it works even if drupal/core is NOT a requirement of the root project

composer.json

@@ -53,6 +53,11 @@
         "discard-changes": true
     },
     "extra": {
+        "composer-drupal-optimizations": {
+            "require": {
+                "symfony/symfony": ">3.4"
+            }
+        },
         "drupal-scaffold": {
             "excludes": [
                 "sites/default/default.settings.php",