patch 8.1.0518: Test_window_split_edit_bufnr() fails on AppVeyor

Problem:    Test_window_split_edit_bufnr() fails on AppVeyor.
Solution:   Disable the failing part for now.
diff --git a/src/version.c b/src/version.c
index b128663..e1c889e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    518,
+/**/
     517,
 /**/
     516,