Presently, gnupg1compat only works with gnupg22. Without this change, the error
```
error: attribute 'version' missing, at .../nixpkgs/pkgs/tools/security/gnupg/1compat.nix:4:26
```
is emitted when evaluating
```
pkgs.gnupg1compat.override { gnupg = pkgs.gnupg20; }'
```