Can't create certificate using env vars

[joevandyk]

$ echo $NERVES_HUB_CERT
-----BEGIN CERTIFICATE-----
MIIB4jCCA <SNIP>
-----END CERTIFICATE-----

$ echo $NERVES_HUB_KEY
g3QAAAAFZAAKYP <SNIP>

$ mix nerves_hub.device cert create West100      

Nerves environment
  MIX_TARGET:   print_server_rpi3
  MIX_ENV:      dev

NervesHub server: api.nerves-hub.org:443
NervesHub organization: crowdcow
Creating certificate for West100
** (MatchError) no match of right hand side value: {:error, :not_found}
    (x509 0.8.1) lib/x509/private_key.ex:215: X509.PrivateKey.from_pem!/2
    (nerves_hub_cli 0.9.1) lib/mix/nerves_hub/shell.ex:40: Mix.NervesHubCLI.Shell.request_auth/1
    (nerves_hub_cli 0.9.1) lib/mix/tasks/nerves_hub.device.ex:350: Mix.Tasks.NervesHub.Device.cert_create/5
    (mix 1.10.2) lib/mix/task.ex:330: Mix.Task.run_task/3
    (mix 1.10.2) lib/mix/cli.ex:82: Mix.CLI.run_task/2