Update GetSegments.java

[buttash]

Update model to match API response....

Proposed fix for [https://github.com//issues/4].

The getSegments now returns correctly with this change. To test I had to make changes to getSegmentsTest within ContactsApiTest as it was erroring with null limit and offset...As I could not work out how to use API credentials within this test module I added them explicitly to the test.

       Long limit = 10l;
        Long offset = 0l;
        String sort = null;
        ApiClient client = new ApiClient();
        client.setApiKey("MY-API-KEY");
        api.setApiClient(client);
       GetSegments response = api.getSegments(limit, offset, sort);