Missing void in _new_stack()

This removes the GCC warning:
"warning: function declaration isn’t a prototype [-Wstrict-prototypes]"
diff --git a/skeletons/OCTET_STRING.c b/skeletons/OCTET_STRING.c
index 3e0f115..7e87068 100644
--- a/skeletons/OCTET_STRING.c
+++ b/skeletons/OCTET_STRING.c
@@ -157,7 +157,7 @@
 }
 
 static struct _stack *
-_new_stack() {
+_new_stack(void) {
 	return (struct _stack *)CALLOC(1, sizeof(struct _stack));
 }