patch 8.0.0288: errors reported while running tests

Problem:    Errors reported while running tests.
Solution:   Put comma in the right place.
diff --git a/src/testdir/runtest.vim b/src/testdir/runtest.vim
index c2260c7..430b89a 100644
--- a/src/testdir/runtest.vim
+++ b/src/testdir/runtest.vim
@@ -158,7 +158,7 @@
       \ 'Test_communicate()',
       \ 'Test_nb_basic()',
       \ 'Test_pipe_through_sort_all()',
-      \ 'Test_pipe_through_sort_some()'
+      \ 'Test_pipe_through_sort_some()',
       \ 'Test_reltime()',
       \ ]