hash-slinger: stay with python2

Seems hard to check whether this one will work with python3.

pkgs/tools/security/hash-slinger/default.nix

@@ -1,7 +1,7 @@
-{ lib, stdenv, fetchFromGitHub, pythonPackages, unbound, libreswan }:
+{ lib, stdenv, fetchFromGitHub, python2Packages, unbound, libreswan }:
 
 let
-  inherit (pythonPackages) python;
+  pythonPackages = python2Packages;
 in stdenv.mkDerivation rec {
   pname    = "hash-slinger";
   version = "2.7";
@@ -31,7 +31,7 @@ in stdenv.mkDerivation rec {
     '';
 
   installPhase = ''
-    mkdir -p $out/bin $out/man $out/${python.sitePackages}/
+    mkdir -p $out/bin $out/man $out/${pythonPackages.python.sitePackages}/
     make install
     wrapPythonPrograms
    '';