[ Fix #531 ] Trim github pr plugin store paths.

Dependencies

• [2] FCNC325Z GithubPulls: Add 'revision' to the input
• [3] CWUG4XMB fix github pulls json to be deterministic
• [4] D5YPJDT6 Add GithubPulls input plugin.

Change contents

• replacement in src/lib/Hydra/Plugin/GithubPulls.pm at line 59
  [3.127]→[3.127:201](∅→∅),[3.201]→[4.1991:2056](∅→∅),[4.1991]→[4.1991:2056](∅→∅)
  − my $storePath = `nix-store --add "$tempdir/github-pulls-sorted.json"`

  − or die "cannot copy path $filename to the Nix store.\n";
  [3.127]

  [2.25]
  + my $storePath = trim(`nix-store --add "$tempdir/github-pulls-sorted.json"`

  + or die "cannot copy path $filename to the Nix store.\n");