2.2.0 release not available on FTP server

**Description of the problem**

https://www.generic-mapping-tools.org/download/ links to [DCW 2.2.0](https://github.com/GenericMappingTools/dcw-gmt/releases/download/2.2.0/dcw-gmt-2.2.0.tar.gz), which is a GitHub release artifact.

These are unfortunately unusable for the Debian package which still relies on the FTP server to find the downloads.

The release checklist includes:
> Run make place-dcw to place the zip file on the dcw ftp and website (@pwessel).

But dcw-gmt-2.1.2.tar.gz is still the most release DCW release on the FTP server.