Use haskell-nix-example/nix branch for nix-tools#2150

hamishmack merged 2 commits intomasterinput-output-hk/haskell.nix:masterfrom

hkm/use-github-static-nix-toolsinput-output-hk/haskell.nix:hkm/use-github-static-nix-toolsCopy head branch name to clipboard