python.pkgs.ftfy: disable on python2

pkgs/development/python-modules/ftfy/default.nix

@@ -1,5 +1,6 @@
 { stdenv
 , buildPythonPackage
+, isPy3k
 , fetchPypi
 , html5lib
 , wcwidth
@@ -15,6 +16,7 @@ buildPythonPackage rec {
   # python 2 and 3, they have pinned ftfy to the v4 branch.
   # I propose to stick to v4 until another package requires v5.
   # At that point we can make a ftfy_v4 package.
+  disabled = !isPy3k;
 
   src = fetchPypi {
     inherit pname version;