Fetching Simple JSON String Array using Retrofit

I want to fetch JSON string array from server using Retrofit. The JSON array is like this.

["A","B","C"]

Here is the code I made .

MainActivity.class

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    String url="http://proverbs-app.antjan.us";

    RestAdapter restAdapter;        
    restAdapter = new RestAdapter.Builder()
    .setEndpoint(url)
    .build(); 

    Service service=restAdapter.create(Service.class);
    service.get(new Callback<List<String>>(){


        @Override

        public void failure(RetrofitError error) {
            Toast.makeText(getApplicationContext(), "Error", Toast.LENGTH_LONG).show();
         }

        @Override
        public void success(List<String> arg0, Response arg1) {
            Toast.makeText(getApplicationContext(), arg0.toString(), Toast.LENGTH_LONG).show();

        }
         });    
}

}

Here is the Service.class

public interface Service {
@GET("/")
public void get(Callback<List<String>> callback);

}

It shows only "Error" Toast.

Am I something wrong with my codes. Please help me to fix it. I'm a beginner. So,please answer me in detail because I don't know much about it. Thanks in advance.