fix missing import of Nix::Store for isValidPath

Dependencies

• [2] SZYDW2DG hydra: added some user admin
• [*] J5UVLXOK * Start of a basic Catalyst web interface.
• [*] SMM4HQTP * Put actions related to builds under /build (e.g. /log/<buildid>

Change contents

• edit in src/lib/Hydra/Controller/Root.pm at line 9
  [2.3041]

  [5.0]
  + use Nix::Store;