patch 8.1.1522: poup_notification() not implemented yet

Problem:    Popup_notification() not implemented yet.
Solution:   Implement it.
diff --git a/src/version.c b/src/version.c
index 28877cb..9c4d068 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1522,
+/**/
     1521,
 /**/
     1520,