update.nix: Run update scripts in parallel

To make updating large attribute sets faster, the update scripts
are now run in parallel.

Please note the following changes in semantics:

- The string passed to updateScript needs to be a path to an executable file.
- The updateScript can also be a list: the tail elements will then be passed
  to the head as command line arguments.

1 files changed, 1 insertions, 0 deletions

diff --git a/pkgs/development/tools/build-managers/gup/default.nix b/pkgs/development/tools/build-managers/gup/default.nix
index f6d5b7b9b59c..7fd801488311 100644
--- a/pkgs/development/tools/build-managers/gup/default.nix
+++ b/pkgs/development/tools/build-managers/gup/default.nix
@@ -16,6 +16,7 @@ stdenv.mkDerivation rec {
     cp -r python/bin $out/bin
   '';
   passthru.updateScript = ''
+    #!${stdenv.shell}
     set -e
     echo
     cd ${toString ./.}