Bump copyright dates.
diff --git a/lib/zip_io_util.c b/lib/zip_io_util.c
index 77be8f0..53f4437 100644
--- a/lib/zip_io_util.c
+++ b/lib/zip_io_util.c
@@ -1,6 +1,6 @@
 /*
  zip_io_util.c -- I/O helper functions
- Copyright (C) 1999-2016 Dieter Baron and Thomas Klausner
+ Copyright (C) 1999-2018 Dieter Baron and Thomas Klausner
 
  This file is part of libzip, a library to manipulate ZIP archives.
  The authors can be contacted at <libzip@nih.at>