Update copyright notice

Author: jesseposner

src/modules/frost/main_impl.h

@@ -1,5 +1,5 @@
 /**********************************************************************
- * Copyright (c) 2021 Jesse Posner                                    *
+ * Copyright (c) 2021 Jesse Posner, Andrew Poelstra                   *
  * Distributed under the MIT software license, see the accompanying   *
  * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
  **********************************************************************/