ytop: Add "ytop" to ytop's error message
ytop: Add "ytop" to ytop's error message

Right now, running `nixos-rebuild` gives an obscure error:
```
$ nixos-rebuild switch
building Nix...
building the system configuration...
error: Abandoned by upstream. Consider switching to bottom instead
(use '--show-trace' to show detailed location information)
```

(And `--show-trace` adds no useful information.)

The error message doesn't indicate that `ytop` is what's causing the problem.
By adding `ytop` to the error message, configurations that still reference
`ytop` will be easier to debug and fix.
NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs