public interface GithubService {
    @GET("/repos/{owner}/{repo}/contributors")
    public List<Contributor> contributors(@Path("owner") String owner, @Path("repo") String repo);
}

RestAdapter restAdapter = new RestAdapter.Builder().setEndpoint("https://api.github.com").build();
GithubService service = restAdapter.create(GithubService.class);
listContributors = service.contributors(username, "retrofit");
Log.d("List Contributors", listContributors+" ");

public class Contributor {
    String login;
    int contributions;
}