patch 8.1.0031: terminal test aucmd_on_close if flaky

Problem:    Terminal test aucmd_on_close if flaky.
Solution:   Wait a bit longer.
diff --git a/src/version.c b/src/version.c
index d13bcfd..846ac70 100644
--- a/src/version.c
+++ b/src/version.c
@@ -762,6 +762,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    31,
+/**/
     30,
 /**/
     29,