Use getter instead fo inline cast

Author: n1ru4l

Diff for: lib/xml-template-builder.js

@@ -44,7 +44,7 @@ exports.buildBucketQuery = function(options, data) {
       ...data.objects.map(object => ({
         Contents: {
           Key: object.key,
-          LastModified: new Date(object.metadata["last-modified"]).toISOString(),
+          LastModified: object.lastModifiedDate.toISOString(),
           ETag: object.metadata["etag"],
           Size: object.size,
           StorageClass: "STANDARD",