Motivation for this change

KinD fixed an issue where docker restart would cause the Kubernetes instance to fail in 0.8.0: kubernetes-sigs/kind#148. This PR bumps the nix version to 0.8.1.

There actually seems to be an issue with building this package with the vgo2nix generated deps.nix file, it fails with the following error but I've yet to trace down the problem:

.......
building
go/src/sigs.k8s.io/kind/pkg/cluster/internal/patch/json6902patch.go:20:2: cannot find package "github.com/evanphx/json-patch/v5" in any of:
        /nix/store/1r61f7iwqfb6dm1krqpj9cjfifjnfmjx-go-1.14.2/share/go/src/github.com/evanphx/json-patch/v5 (from $GOROOT)
        /build/go/src/github.com/evanphx/json-patch/v5 (from $GOPATH)
builder for '/nix/store/skv11yxvpsy8zcyiqba8gcar83wdiyy4-kind-0.8.1.drv' failed with exit code 1

Instead, what I did is update the nix file to use the new buildGoModule system instead. This appears to work.

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.