stress-ng 0.04.20 -> 0.04.21

(cherry picked from commit 6d7273571c8f71e49e406227206b35312074a714)

pkgs/tools/system/stress-ng/default.nix

···
 { stdenv, fetchurl, attr, keyutils }:
 
 let
-  version = "0.04.20";
+  version = "0.04.21";
   name = "stress-ng-${version}";
 in stdenv.mkDerivation {
   inherit name;
 
   src = fetchurl {
-    sha256 = "0zzlnqmld804h08iabhcrj3ggm5wiry9g2jrdr33cqp44lrw402v";
+    sha256 = "01308c31dx7ln7w3r74f18c473hz9236f118b27z1js94dsya0hw";
     url = "http://kernel.ubuntu.com/~cking/tarballs/stress-ng/${name}.tar.gz";
   };