add customary EOF \n to written JSON

Signed-off-by: Brian S. Stephan <bss@incorporeal.org>

gp2040ce_bintools/builder.py

@@ -251,7 +251,7 @@ def write_new_config_to_filename(config: Message, filename: str, inject: bool =
     else:
         if filename[-5:] == '.json':
             with open(filename, 'w') as file:
-                file.write(MessageToJson(config))
+                file.write(f'{MessageToJson(config)}\n')
         else:
             binary = storage.serialize_config_with_footer(config)
             with open(filename, 'wb') as file: