Attempt to fix update-nix

Author: jonringer

update-nix.sh

@@ -1,11 +1,7 @@
-#!/usr/bin/env nix-shell
-#!nix-shell -p nixUnstable -i bash
+#!/usr/bin/env bash
 
 set -e
 
-# need to overwrite buildkite's version
-NIX_UNSTABLE=$(nix-build '<nixpkgs>' -A nixUnstable)/bin/nix
-
 name=$(basename $0)
 
 usage() {