patch 8.0.0811: MS-Windows: test_expand_dllpath fails

Problem:    MS-Windows: test_expand_dllpath fails.
Solution:   Change backslashes to forward slashes
diff --git a/src/version.c b/src/version.c
index fa67f7f..90d9273 100644
--- a/src/version.c
+++ b/src/version.c
@@ -770,6 +770,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    811,
+/**/
     810,
 /**/
     809,