t/harness: Run tests for IO::Zlib sequentially

Most of these failed for me in one run inexplicably.  This typically
means there was a glitch, and its likely to be that the tests somehow
interferred with each other.  Rather than take the time to investigate
further, I changed harness to run the tests for this distribution
sequentially.

1 files changed, 1 insertions, 1 deletions

diff --git a/t/harness b/t/harness
index 7733d2bb78..84e3d57bbb 100644
--- a/t/harness
+++ b/t/harness
@@ -189,7 +189,7 @@ if (@ARGV) {
         # directory containing such files should be tested in serial order.
         #
         # Add exceptions to the above rule
-        for (qw(ext/Pod-Html/t)) {
+        for (qw(ext/Pod-Html/t cpan/IO-Zlib)) {
             $serials{$_} = 1;
         }