So siehts ganz gut aus !

node_modules/core-js/modules/es6.reflect.is-extensible.js

@@ -0,0 +1,11 @@
+// 26.1.10 Reflect.isExtensible(target)
+var $export = require('./_export');
+var anObject = require('./_an-object');
+var $isExtensible = Object.isExtensible;
+
+$export($export.S, 'Reflect', {
+  isExtensible: function isExtensible(target) {
+    anObject(target);
+    return $isExtensible ? $isExtensible(target) : true;
+  }
+});