Restore path in nix-shell

Dependencies

• [2] X7IAG7JT Simplify running nix-shell
• [*] T4LLYESZ * Nix expression for building Hydra.

Change contents

• edit in release.nix at line 148
  [2.987]

  [2.987]
  + preHook = ''

  + PATH=$(pwd)/src/script:$(pwd)/src/hydra-eval-jobs:$(pwd)/src/hydra-queue-runner:$PATH

  + PERL5LIB=$(pwd)/src/lib:$PERL5LIB;

  + '';

  +