Merge branch 'update-nixpkgs' into 'develop'

Weekly nixpkgs update.

See merge request privatestorage/PrivateStorageio!221

nixpkgs-2105.json

 {
   "name": "release2105",
-  "url": "https://releases.nixos.org/nixos/21.05/nixos-21.05.4114.195d5816cdd/nixexprs.tar.xz",
-  "sha256": "1074fy0as55vxqy36rqs33hvdqf92ys5di6ij826h34b5qvcfjkm"
+  "url": "https://releases.nixos.org/nixos/21.05/nixos-21.05.4388.a284564b7f7/nixexprs.tar.xz",
+  "sha256": "1wf7m96b1wxhkkkpf5dn0gxf4mcf1ay2v8lw0mdlhdk3gfzg6v76"
 }
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