Add dependency on Switch.

Dependencies

• [2] AMFMXR52 Provide a command ‘hydra-init’ to initialise/upgrade the database
• [*] SAFVRDTK * Put Hydra's dependencies so that they can easily be installed in a
• [*] 3YSK5YXG * Update to Catalyst 5.9.

Change contents

• edit in deps.nix at line 32
  [5.23]

  [2.495]
  + perlPackages.Switch # XXX: seems to be an indirect dep of `hydra-build'