Fix with nettle >=4

Index: lib/rc-md5.h
--- lib/rc-md5.h.orig
+++ lib/rc-md5.h
@@ -13,7 +13,7 @@
 
 #ifdef HAVE_NETTLE
 
-#include <nettle/md5-compat.h>
+#include <nettle/md5.h>
 
 #else
 
