use resource from own package

I use sdk-version-3.20.0 tag as a gradle module.
Such error came out when I build.

```
/Users/waka/projects/app/modules/facebook/facebook/src/com/facebook/internal/ImageDownloader.java:262: エラー: パッケージRは存在しません
                        errorMessageBuilder.append(R.string.com_facebook_image_download_unknown_error);
```