api/v3: Due date is missing in issues response

Make request like this:

• curl -H "PRIVATE-TOKEN: token" https://gitlab.example.com/api/v3/projects/1/issues

Results

• Actual result:

[
...
   {
        "assignee": nil,
        "author": {
            "avatar_url": "url",
            "id": 8,
            "name": "name",
            "state": "active",
            "username": "name",
            "web_url": "url"
        },
        "created_at": "2016-01-01T13:00:25.079Z",
        "description": "issue description ",
        "id": 2,
        "iid": 1,
        "labels": [
            "label1",
            "label2"
        ],
        "milestone": null,
        "project_id": 1,
        "state": "opened",
        "subscribed": false,
        "title": "Investigate ...",
        "updated_at": "2016-01-01T00:48:05.935Z",
        "user_notes_count": 0
    },
...
]

• Actual result: (should contain "due_date" field)

[
...
   {
        "assignee": nil,
        "author": {
            "avatar_url": "url",
            "id": 8,
            "name": "name",
            "state": "active",
            "username": "name",
            "web_url": "url"
        },
        "created_at": "2016-01-01T13:00:25.079Z",
        "description": "issue description ",
        "id": 2,
        "iid": 1,
        "labels": [
            "label1",
            "label2"
        ],
        "milestone": null,
        "project_id": 1,
        "state": "opened",
        "subscribed": false,
        "title": "Investigate ...",
        "updated_at": "2016-01-01T00:48:05.935Z",
        "user_notes_count": 0,
        "due_date": "2016-01-05"
    },
...
]