patch 8.1.1525: cannot move a popup window with the mouse

Problem:    Cannot move a popup window with the mouse.
Solution:   Add the "drag" property and make it possible to drag a popup
            window by its border.
diff --git a/src/version.c b/src/version.c
index 9835fcc..058dbc7 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1525,
+/**/
     1524,
 /**/
     1523,