Shut up some Perl 5.20 warnings

Dependencies

• [2] FG4JZPWS Handle builds with multiple outputs correctly in Hydra channels
• [3] KSBB33RE Add a dashboard
• [4] XJRJ4J7M Add user registration
• [5] 4CELXP7P Remove the longDescription field
• [6] L5Z6CN7M In Hydra channels, show only packages matching the user's system type
• [7] PF72JKWQ Add a "My jobs" tab to the dashboard
• [*] LVJKRTIK * Generate a Nix expression for the channel.

Change contents

• replacement in src/lib/Hydra/Controller/User.pm at line 309
  [3.1161]→[3.1161:1241](∅→∅)
  − push $c->stash->{starredJobs}, { job => $j->job, builds => [@builds] };
  [3.1161]

  [3.1241]
  + push @{$c->stash->{starredJobs}}, { job => $j->job, builds => [@builds] };
• replacement in src/lib/Hydra/View/NixExprs.pm at line 62
  [2.2245]→[2.2245:2298](∅→∅)
  − foreach my $job (keys $perSystem{$system}) {
  [2.2245]

  [2.2298]
  + foreach my $job (keys %{$perSystem{$system}}) {
• replacement in src/lib/Hydra/View/NixExprs.pm at line 81
  [2.3376]→[2.3376:3435](∅→∅)
  − my @outputNames = sort (keys $pkg->{outputs});
  [2.3376]

  [2.3435]
  + my @outputNames = sort (keys %{$pkg->{outputs}});