me_cleaner: stay with python2

pkgs/tools/misc/me_cleaner/default.nix

···
-{ lib, buildPythonPackage, fetchFromGitHub }:
+{ lib, python2, fetchFromGitHub }:
 
-buildPythonPackage rec {
+python2.pkgs.buildPythonPackage rec {
   pname = "me_cleaner";
   version = "1.2";
 

pkgs/top-level/all-packages.nix

···
     stdenv = if stdenv.cc.isClang then llvmPackages_5.stdenv else stdenv;
   };
 
-  me_cleaner = pythonPackages.callPackage ../tools/misc/me_cleaner { };
+  me_cleaner = callPackage ../tools/misc/me_cleaner { };
 
   mesos-dns = callPackage ../servers/mesos-dns { };