Add copyright holder

This commit adds "Smallstep Labs, Inc." as the copyright holder in the
LICENSE file.

Fixes #192

Author: maraino

LICENSE

@@ -186,7 +186,7 @@
       same "printed page" as the copyright notice for easier
       identification within third-party archives.
 
-   Copyright [yyyy] [name of copyright owner]
+   Copyright 2025 Smallstep Labs, Inc.
 
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.