nixos/sd-image: explicit reference to the gawk package
nixos/sd-image: explicit reference to the gawk package

The `awk` command is not installed in the standard env. So this command fails if the `awk` command is not installed by some external module.

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