[Nix-dev] upgrading packer

[Samuel]

> Sorry, I made it sound more easy that it was. For some reason I thought they
> had vendored all the dependencies.
>
> I took a stab at the update yesterday and here is the PR:
> https://github.com/NixOS/nixpkgs/pull/15426/files

Awesome, thanks!

> What I had to do was checkout packer at the specific tag, run `godep
> restore` and then `go2nix save`. Copy the generated `default.nix` to
> overwrite the `deps.nix` file. And then the tricky part was to get packer to
> build properly using all of this since they have a custom build pipeline.

Might make sense to dump this into a script (or a comment in the worst
case) along with the derivation.

-- 
Samuel