python3Packages.sphinx: add missing dep packaging

+2
+2
pkgs/development/python-modules/sphinx/default.nix
··· 28 28 , sphinxcontrib-websupport 29 29 , typing 30 30 , setuptools 31 + , packaging 31 32 }: 32 33 33 34 buildPythonPackage rec { ··· 52 53 pygments 53 54 alabaster 54 55 Babel 56 + packaging 55 57 setuptools 56 58 snowballstemmer 57 59 six