Use Nix::Store and Nix::Utils in NARInfo.pm

These are required for the `signString` and `readFile` subroutines used when signing NARs.

(cherry picked from commit b94a7b6d5c)

src/lib/Hydra/View/NARInfo.pm

@@ -6,6 +6,8 @@ use File::Basename;
 use Hydra::Helper::CatalystUtils;
 use MIME::Base64;
 use Nix::Manifest;
+use Nix::Store;
+use Nix::Utils;
 use Hydra::Helper::Nix;
 use base qw/Catalyst::View/;