patch 8.1.1771: options test fails on MS-Windows

Problem:    Options test fails on MS-Windows.
Solution:   Add correct and incorrect values for 'completeslash'.
diff --git a/src/version.c b/src/version.c
index b0fe67f..5507f6a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1771,
+/**/
     1770,
 /**/
     1769,