$NERVES_HUB_CA_DIR is not respected

[ConnorRigby]

  defp ca_certs() do
    [
      "/home/connor/workspace/oss/elixir/nerves/nerves-hub/ssl/ca.pem"
    ]
    |> Enum.map(&File.read!/1)
    |> Enum.map(&Certificate.from_pem!/1)
    |> Enum.map(&Certificate.to_der/1)
  end

Had to do this to get CA certs to load