gopass: Use latest buildGoPackage

[rvolosatovs]

Motivation for this change

Go 1.10 is marked as broken on Darwin(see https://github.com/NixOS/nixpkgs/pull/56744/files#diff-0ed9de1390061094a04a4f8c69e29a87R185 in #56744)
There's no reason not to use the latest available Go version to build gopass though, since it builds just fine.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• 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 nix-review --run "nix-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)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.

---

[marsam]

built and tested locally on NixOS and Darwin
Thanks!