uwsgi: add a type comment

Changed files
+1
pkgs
servers
uwsgi
+1
pkgs/servers/uwsgi/default.nix
···
{ stdenv, lib, fetchurl, pkgconfig, jansson
+
# plugins: list of strings, eg. [python2, python3]
, plugins
, pam, withPAM ? stdenv.isLinux
, systemd, withSystemd ? stdenv.isLinux