Updated authors

testing/diff_output_files.py

@@ -1,5 +1,6 @@
 # Copyright (C) 2015-2025: The University of Edinburgh, United Kingdom
-#                 Authors: Craig Warren, Antonis Giannopoulos, and John Hartley
+#                 Authors: Craig Warren, Antonis Giannopoulos, John Hartley, 
+#                          and Nathan Mannall
 #
 # This file is part of gprMax.
 #