fpm seems to be broken

[copumpkin]

Issue description

Running fpm results in a crash as follows:

$ result/bin/fpm
/nix/store/0lwpkxcnnsv92i48ms94dvhhfib6bba4-fpm-1.4.0/lib/ruby/gems/2.3.0/gems/ffi-1.9.10/lib/ffi/library.rb:263:in `attach': unhandled exception
    from /nix/store/0lwpkxcnnsv92i48ms94dvhhfib6bba4-fpm-1.4.0/lib/ruby/gems/2.3.0/gems/ffi-1.9.10/lib/ffi/library.rb:263:in `attach_function'
    from /nix/store/0lwpkxcnnsv92i48ms94dvhhfib6bba4-fpm-1.4.0/lib/ruby/gems/2.3.0/gems/fpm-1.4.0/lib/fpm/util.rb:16:in `rescue in <module:Util>'
    from /nix/store/0lwpkxcnnsv92i48ms94dvhhfib6bba4-fpm-1.4.0/lib/ruby/gems/2.3.0/gems/fpm-1.4.0/lib/fpm/util.rb:12:in `<module:Util>'
    from /nix/store/0lwpkxcnnsv92i48ms94dvhhfib6bba4-fpm-1.4.0/lib/ruby/gems/2.3.0/gems/fpm-1.4.0/lib/fpm/util.rb:6:in `<top (required)>'
    from /nix/store/0lwpkxcnnsv92i48ms94dvhhfib6bba4-fpm-1.4.0/lib/ruby/gems/2.3.0/gems/fpm-1.4.0/lib/fpm/package.rb:2:in `require'
    from /nix/store/0lwpkxcnnsv92i48ms94dvhhfib6bba4-fpm-1.4.0/lib/ruby/gems/2.3.0/gems/fpm-1.4.0/lib/fpm/package.rb:2:in `<top (required)>'
    from /nix/store/0lwpkxcnnsv92i48ms94dvhhfib6bba4-fpm-1.4.0/lib/ruby/gems/2.3.0/gems/fpm-1.4.0/lib/fpm.rb:3:in `require'
    from /nix/store/0lwpkxcnnsv92i48ms94dvhhfib6bba4-fpm-1.4.0/lib/ruby/gems/2.3.0/gems/fpm-1.4.0/lib/fpm.rb:3:in `<top (required)>'
    from /nix/store/0lwpkxcnnsv92i48ms94dvhhfib6bba4-fpm-1.4.0/lib/ruby/gems/2.3.0/gems/fpm-1.4.0/bin/fpm:5:in `require'
    from /nix/store/0lwpkxcnnsv92i48ms94dvhhfib6bba4-fpm-1.4.0/lib/ruby/gems/2.3.0/gems/fpm-1.4.0/bin/fpm:5:in `<top (required)>'
    from result/bin/fpm:18:in `load'
    from result/bin/fpm:18:in `<main>'

Steps to reproduce

1. Get nixpkgs 3a542c7
2. Run nix-build -A fpm from your clone
3. Run ./result/bin/fpm
4. Be sad

cc @vcunat who added the package

Other stuff

I'm running this on NixOS, on x86_64.

[copumpkin]

Hmm, this doesn't seem to be broken on my machine anymore, even on the same commit. I guess I should be worried, but I'll just close this for now.

[vcunat]

I don't think anything similar has ever happened to me.