libi3: change scalloc() signature to match calloc()

src/con.c

@@ -36,7 +36,7 @@ void con_force_split_parents_redraw(Con *con) {
  *
  */
 Con *con_new_skeleton(Con *parent, i3Window *window) {
-    Con *new = scalloc(sizeof(Con));
+    Con *new = scalloc(1, sizeof(Con));
     new->on_remove_child = con_on_remove_child;
     TAILQ_INSERT_TAIL(&all_cons, new, all_cons);
     new->aspect_ratio = 0.0;