patch 8.0.1521: Shift-Tab does not work in a terminal window

Problem:    Shift-Tab does not work in a terminal window.
Solution:   Recognize Shift-Tab key press. (Jsees Luehrs, closes #2644)
diff --git a/src/version.c b/src/version.c
index c7240f1..405e3b5 100644
--- a/src/version.c
+++ b/src/version.c
@@ -772,6 +772,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1521,
+/**/
     1520,
 /**/
     1519,