patch 8.1.1589: popup window does not indicate scroll position

Problem:    Popup window does not indicate scroll position.
Solution:   Add a scrollbar.
diff --git a/src/version.c b/src/version.c
index 3f3d77f..34af0de 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1589,
+/**/
     1588,
 /**/
     1587,