Motivation for this change

Type systemctl rest<TAB> in fish and you get the following error message:

 archachatina  ~  systemctl restart diInteger 243 in '243 (243)' followed by non-digit           Fri 17 Jan 2020 05:43:35 PM CET
        Integer 243 in '243 (243)' followed by non-digit

(The error message is shown twice and messes up the prompt, which drives me crazy.)

Unfortunately it's not clear when the next fish release is going to be (see fish-shell/fish-shell#5934), so I'd like to patch this now.

cc maintainer @ocharles

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.