Ensure your application has the latest copy of MaxMind data when deploying. Ideally, you should have a way to restart your application to make sure this build back happens often enough (if you deploy daily/weekly, you have nothing to worry about).
The database file(s) is saved to a Heroku cache directory that is persisted across builds. If the database file does not exist, or is older than a week, a new copy is downloaded and moved to your project before deployment. If MAXMIND_DB_DIR is set, database files are stored there when deployed. Otherwise, files are stored in the root of your project.
Follow the instructions at https://github.com/ddollar/heroku-buildpack-multi for using multiple build packs. Simply add this repository to this list and wallah!
Copy the snippet above into CLI.