sent: enable on darwin

pkgs/applications/misc/sent/default.nix

···
 , patches ? [] }:
 
 stdenv.mkDerivation rec {
-  name = "sent-1";
+  pname = "sent";
+  version = "1";
 
   src = fetchurl {
-    url = "https://dl.suckless.org/tools/${name}.tar.gz";
+    url = "https://dl.suckless.org/tools/sent-${version}.tar.gz";
     sha256 = "0cxysz5lp25mgww73jl0mgip68x7iyvialyzdbriyaff269xxwvv";
   };
 
···
     description = "A simple plaintext presentation tool";
     homepage = "https://tools.suckless.org/sent/";
     license = licenses.isc;
-    platforms = platforms.linux;
+    platforms = platforms.unix;
     maintainers = with maintainers; [ pSub ];
   };
 }