A large CircleCI VM can able to handle 4 test jobs

rather than 2. Possibly we could run more in parallel. Might be worth
experimenting with.

.circleci/config.yml

@@ -62,7 +62,7 @@ jobs:
       - run:
           command: |
             pushd metacpan-docker
-            docker-compose exec -T api_test env HARNESS_PERL_SWITCHES="-MDevel::Cover=+ignore,^t/|^test-data/|^etc/" prove -lr --jobs 2 t
+            docker-compose exec -T api_test env HARNESS_PERL_SWITCHES="-MDevel::Cover=+ignore,^t/|^test-data/|^etc/" prove -lr --jobs 4 t
           name: run tests with coverage
       # The report ends up being owned by root. We need to chown it so that
       # the cover command can make changes to it.