Without this I was getting errors like:
> error: flake 'flake:nixos-anywhere' does not provide attribute 'packages.x86_64-linux.nixosConfigurations."digitalocean".config.system.build.diskoScript', 'legacyPackages.x86_64-linux.nixosConfigurations."digitalocean".config.system.build.diskoScript' or 'nixosConfigurations."digitalocean".config.system.build.diskoScript'
I'm not sure why.