koji: use python2

pkgs/tools/package-management/koji/default.nix

···
-{ stdenv, fetchurl, pythonPackages, python }:
+{ stdenv, fetchurl, python2 }:
 
-stdenv.mkDerivation rec {
+let
+  pythonEnv = python2.withPackages(ps : [ps.pycurl]);
+in stdenv.mkDerivation rec {
   name = "koji-1.8";
 
   src = fetchurl {
···
     sha256 = "10dph209h4jgajb5jmbjhqy4z4hd22i7s2d93vm3ikdf01i8iwf1";
   };
 
-  propagatedBuildInputs = [ pythonPackages.pycurl python ];
+  propagatedBuildInputs = [ pythonEnv ];
 
   makeFlags = "DESTDIR=$(out)";