Buildkite: really fix dependencies of check-hydra script

Fix for #163 was missing something.

Failure was random because the repo is often already unpacked due to
the daily Hackage and Stackage update process.

Author: rvl

scripts/check-hydra.nix

@@ -7,7 +7,7 @@ writeScript "check-hydra.sh" ''
 
   set -euo pipefail
 
-  export PATH="${makeBinPath [ coreutils time gnutar hydra jq  ]}"
+  export PATH="${makeBinPath [ coreutils time gnutar gzip hydra jq ]}"
 
   echo '~~~ Evaluating release.nix'
   command time --format '%e' -o eval-time.txt \