nspluginwrapper: add missing libXt build input

pkgs/applications/networking/browsers/mozilla-plugins/nspluginwrapper/default.nix

···
-{stdenv, fetchurl, which, pkgconfig, file, glib, gtk2, gtk3, curl}:
+{stdenv, fetchurl, which, pkgconfig, file, glib, gtk2, gtk3, curl, libXt}:
 let
   srcData = # Generated upstream information 
   rec {
···
     export configureFlags="$configureFlags --target-cpu=$(uname -m)"
   '';
 
-  buildInputs = [which pkgconfig file glib gtk2 gtk3 curl];
+  buildInputs = [which pkgconfig file glib gtk2 gtk3 curl libXt];
 
   preferLocalBuild = true;