update to NixOS 21.05

examples/configuration.nix

@@ -240,7 +240,7 @@
   # compatible, in order to avoid breaking some software such as database
   # servers. You should change this only after NixOS release notes say you
   # should.
-  system.stateVersion = "18.09"; # Did you read the comment?
+  system.stateVersion = "21.05"; # Did you read the comment?
 
   # The nix-bitcoin release version that your config is compatible with.
   # When upgrading to a backwards-incompatible release, nix-bitcoin will display an

modules/presets/hardened.nix

@@ -9,6 +9,6 @@
   # Needed for sandboxed builds and services
   security.allowUserNamespaces = true;
 
-  # The "scudo" allocator is broken on NixOS 20.09
+  # The "scudo" allocator is broken on NixOS >= 20.09
   environment.memoryAllocator.provider = "libc";
 }

pkgs/nixpkgs-pinned.nix

@@ -8,8 +8,9 @@ in
 {
   # To update, run ../helper/fetch-channel REV
   nixpkgs = fetch {
-    rev = "359e6542e1d41eb18df55c82bdb08bf738fae2cf";
-    sha256 = "05v28njaas9l26ibc6vy6imvy7grbkli32bmv0n32x6x9cf68gf9";
+    # nixos-21.05 (2021-08-03)
+    rev = "d4590d21006387dcb190c516724cb1e41c0f8fdf";
+    sha256 = "17q39hlx1x87xf2rdygyimj8whdbx33nzszf4rxkc6b85wz0l38n";
   };
   nixpkgs-unstable = fetch {
     rev = "16105403bdd843540cbef9c63fc0f16c1c6eaa70";