linux: 5.1.20 -> 5.1.21

pkgs/os-specific/linux/kernel/linux-5.1.nix

···
 with stdenv.lib;
 
 buildLinux (args // rec {
-  version = "5.1.20";
+  version = "5.1.21";
 
   # modDirVersion needs to be x.y.z, will automatically add .0 if needed
   modDirVersion = if (modDirVersionArg == null) then concatStrings (intersperse "." (take 3 (splitString "." "${version}.0"))) else modDirVersionArg;
···
 
   src = fetchurl {
     url = "mirror://kernel/linux/kernel/v5.x/linux-${version}.tar.xz";
-    sha256 = "039i5b41dv930kmq8jwskcwjc6r26h9xy7jgbi6aggn0ycyig21d";
+    sha256 = "1xj1wfhjz2s5a8j6zx3fsd7rrrkvw5waszzylf2gn3ag6615yjan";
   };
 } // (args.argsOverride or {}))