bump atc
bump atc

Submodule src/github.com/concourse/atc 189849855..cc2fa8d51:
  > Revert "Create migration for new BTREE index on check_order column of version_resources table."
  > Merge pull request #278 from databus23/prometheus-err-exit
  > clean up logging of gc handles

Signed-off-by: Divya Dadlani <509f062e20590ad33545b76914b972e08ef4d2e0@pivotal.io>

concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse