patch 8.1.0891: substitute command inssuficiently tested

Problem:    Substitute command inssuficiently tested.
Solution:   Add more test coverage. (Dominique Pelle)
diff --git a/src/version.c b/src/version.c
index c865fc0..7de8a0a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -784,6 +784,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    891,
+/**/
     890,
 /**/
     889,