sensu gitlab plugin is not compatible with gitlab version >=12.4

[art-shutter]

As per gitlab's docs here, the JSON payload of response to curl 'https://gitlab.example.com/-/liveness' has changed. It used to provide separate entries (example: {"db_check":{"status":"ok"},"redis_check":{"status":"ok"},"cache_check":{"status":"ok"},"queues_check":{"status":"ok"},"shared_state_check":{"status":"ok"},"gitaly_check":{"status":"ok"}}), but now the response is something like { "status": "ok" } .

I believe there needs to be an update to reflect these breaking changes in GitLab.