Data member isn't present when fetching a relationship

[kocsismate]

As found by @emil-nasso in #20 when visiting the following example url: ?path=/users/2/relationships/contacts, the data member doesn't show up:

{
  "links": {
    "related": "/?path=/users/2/contacts",
    "self": "/?path=/users/2/relationships/contacts"
  }
}

However, when including the relationship in question: ?path=/users/1/relationships/contacts&include=contacts it will be visible:

{
  "links": {
    "related": "/?path=/users/1/contacts",
    "self": "/?path=/users/1/relationships/contacts"
  },
  "data": [
    {
      "type": "contact",
      "id": "100"
    },
    {
      "type": "contact",
      "id": "101"
    },
    {
      "type": "contact",
      "id": "102"
    }
  ],
  "included": [
    {
      "type": "contact",
      "id": "100",
      "links": {
        "self": "/?path=/contacts/100"
      },
      "attributes": {
        "phone": "+123456789"
      }
    },
    {
      "type": "contact",
      "id": "101",
      "links": {
        "self": "/?path=/contacts/101"
      },
      "attributes": {
        "email": "john.doe@example.com"
      }
    },
    {
      "type": "contact",
      "id": "102",
      "links": {
        "self": "/?path=/contacts/102"
      },
      "attributes": {
        "email": "secret.doe@example.com"
      }
    }
  ]
}

[kocsismate]

Fixed in this commit: 1aef043