err: nothing to import

Hello!
When I'm trying:
```sh
mmdbctl import --in geoip2-ipv4.csv --out data.mmdb
```
it returns
```sh
err: nothing to import
```
File here [https://github.com/datasets/geoip2-ipv4/blob/master/data/geoip2-ipv4.csv](https://github.com/datasets/geoip2-ipv4/blob/master/data/geoip2-ipv4.csv)