Use uintptr_t for ipc container id

This is for compatability with i3.

sway/ipc-json.c

@@ -214,7 +214,7 @@ json_object *ipc_json_describe_container(swayc_t *c) {
 
 	json_object *object = json_object_new_object();
 
-	json_object_object_add(object, "id", json_object_new_int((intptr_t)&c));
+	json_object_object_add(object, "id", json_object_new_int((uintptr_t)&c));
 	json_object_object_add(object, "name", (c->name) ? json_object_new_string(c->name) : NULL);
 	json_object_object_add(object, "rect", ipc_json_create_rect(c));
 	json_object_object_add(object, "visible", json_object_new_boolean(c->visible));