Fix program_security_page for python3

In python3 if you read from a file using 'r' you get strings, not bytes.
The API for programming expects bytes, so change accordingly.

programmer/tinyprog/__main__.py

@@ -479,7 +479,7 @@ def progress(info):
                     print("    Programming %s security page with %s" % (
                         active_port, args.security))
 
-                    data = open(args.security, 'r').read()
+                    data = open(args.security, 'rb').read()
 
                     if args.addr is not None:
                         addr = parse_int(args.addr)