Use undefined instead of void 0.

lib/6to5/transformation/templates/get.js

@@ -1,11 +1,11 @@
 (function get(object, property, receiver) {
   var desc = Object.getOwnPropertyDescriptor(object, property);
 
-  if (desc === void 0) {
+  if (desc === undefined) {
     var parent = Object.getPrototypeOf(object);
 
     if (parent === null) {
-      return void 0;
+      return undefined;
     } else {
       return get(parent);
     }
@@ -14,8 +14,8 @@
   } else {
     var getter = desc.get;
 
-    if (getter === void 0) {
-      return void 0;
+    if (getter === undefined) {
+      return undefined;
     }
 
     return getter.call(receiver);