patch 9.0.1550: in cmdline window S-Tab does not select previous completion

Problem:    In cmdline window S-Tab does not select previous completion.
            (Maxim Kim)
Solution:   Add a mappint for S-Tab. (closes #12116)
diff --git a/src/version.c b/src/version.c
index 857a229..923ea97 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1550,
+/**/
     1549,
 /**/
     1548,