Motivation for this change

We use the Gurobi solver for some of our work; it is easy to obtain an academic license, and is typically far superior to open source solvers.

Once logged in, you can download for various platforms including Mac OS X. I do not have OS X nor do I know enough nix to know how to generify the nix expression for OS X.

Things done

I'll try to follow contributing.md more closely once issues are resolved re: OS X and any others that come up, as well as updating Gurobi to the latest version.

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • [ X] 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 nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.