nix: bumped to the HEAD of 21.05

nix/sources.json

@@ -54,10 +54,10 @@
         "homepage": "https://github.com/NixOS/nixpkgs",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "63ee5cd99a2e193d5e4c879feb9683ddec23fa03",
-        "sha256": "0avbsx5chbwr0y55shndkzf0ixx3bznbzq526p5nj8llryxa10af",
+        "rev": "733682c32929293341f113f297b64ea6319e9089",
+        "sha256": "0f6zi45av9s176a2pi15jyf08xk0nsg181hhjhnz3asr0whyarf1",
         "type": "tarball",
-        "url": "https://github.com/NixOS/nixpkgs/archive/63ee5cd99a2e193d5e4c879feb9683ddec23fa03.tar.gz",
+        "url": "https://github.com/NixOS/nixpkgs/archive/733682c32929293341f113f297b64ea6319e9089.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "nixpkgsUnstable": {