Merge branch 'update-nixpkgs' into 'develop'

Update nixpkgs.

See merge request privatestorage/PrivateStorageio!223

nixpkgs-2105.json

 {
   "name": "release2105",
-  "url": "https://releases.nixos.org/nixos/21.05/nixos-21.05.4388.a284564b7f7/nixexprs.tar.xz",
-  "sha256": "1wf7m96b1wxhkkkpf5dn0gxf4mcf1ay2v8lw0mdlhdk3gfzg6v76"
+  "url": "https://releases.nixos.org/nixos/21.05/nixos-21.05.4470.3b422991781/nixexprs.tar.xz",
+  "sha256": "1aly3c42g16mwkcqx1ycyfvmx96k642y1cszjxl0wx79piqn8jdd"
 }
\ No newline at end of file