Default value of public_net in create server is invalid.

[josiasmontag]

The in 2.8.0 introduced default value of [] for public_net is invalid. It is rejected by the Hetzner API:

{
  "error" : {
    "message" : "invalid input in field 'public_net'",
    "code" : "invalid_input",
    "details" : {
      "fields" : [ {
        "name" : "public_net._schema",
        "messages" : [ "root must be an object" ]
      } ]
    }
  }
}

The public_net parameter should be completely omitted by default.

Bug introduced by commit: 48c8ccc

[eugenecooper]

This (or very similar) issue still persits in v2.8.2 (and dev-master)
The error message I get was a bit different though:

{
  "error": {
    "code": "invalid_input",
    "message": "failed to parse json",
    "details": {
      "fields": [
        {
          "name": "public_net",
          "messages": [
            "cannot parse type array as createServerPublicNet"
          ]
        }
      ]
    }
  }
}

The solution proposed by @josiasmontag didn't work for me, so I made another PR #138 that fixes the problem.