patch 8.1.0031: terminal test aucmd_on_close if flaky

Problem:    Terminal test aucmd_on_close if flaky.
Solution:   Wait a bit longer.

src/testdir/test_terminal.vim

@@ -384,7 +384,8 @@ endfunc
 func s:get_sleep_cmd()
   if s:python != ''
     let cmd = s:python . " test_short_sleep.py"
-    let waittime = 500
+    " 500 was not enough for Travis
+    let waittime = 900
   else
     echo 'This will take five seconds...'
     let waittime = 2000

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    31,
 /**/
     30,
 /**/