tor: initial updateScript

Tested briefly, seems to work okay. The gpg stuff could be better,
however.

pkgs/tools/security/tor/default.nix

@@ -1,5 +1,17 @@
 { stdenv, fetchurl, pkgconfig, libevent, openssl, zlib, torsocks
 , libseccomp, systemd, libcap
+
+# for update.nix
+, writeScript
+, runCommand
+, common-updater-scripts
+, bash
+, coreutils
+, curl
+, gnugrep
+, gnupg
+, gnused
+, nix
 }:
 
 stdenv.mkDerivation rec {
@@ -34,6 +46,22 @@ stdenv.mkDerivation rec {
 
   doCheck = true;
 
+  passthru.updateScript = import ./update.nix {
+    inherit (stdenv) lib;
+    inherit
+      writeScript
+      runCommand
+      common-updater-scripts
+      bash
+      coreutils
+      curl
+      gnupg
+      gnugrep
+      gnused
+      nix
+    ;
+  };
+
   meta = with stdenv.lib; {
     homepage = https://www.torproject.org/;
     repositories.git = https://git.torproject.org/git/tor;