btrfs-heatmap: modernize a bit

pkgs/by-name/bt/btrfs-heatmap/package.nix

@@ -13,7 +13,7 @@ stdenv.mkDerivation (finalAttrs: {
   src = fetchFromGitHub {
     owner = "knorrie";
     repo = "btrfs-heatmap";
-    rev = "v${finalAttrs.version}";
+    tag = "v${finalAttrs.version}";
     sha256 = "sha256-yCkuZqWwxrs2eS7EXY6pAOVVVSq7dAMxJtf581gX8vg=";
   };
 
@@ -40,6 +40,10 @@ stdenv.mkDerivation (finalAttrs: {
     runHook postInstall
   '';
 
+  strictDeps = true;
+  __structuredAttrs = true;
+  enableParallelBuilding = true;
+
   meta = {
     description = "Visualize the layout of a mounted btrfs";
     mainProgram = "btrfs-heatmap";