patch 8.1.0781: build error when using if_xcmdsrv.c

Problem:    Build error when using if_xcmdsrv.c.
Solution:   Add missing part of 8.1.0779.
diff --git a/src/version.c b/src/version.c
index 946a6a2..b62aa35 100644
--- a/src/version.c
+++ b/src/version.c
@@ -792,6 +792,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    781,
+/**/
     780,
 /**/
     779,