dos2unix: add meta.platforms

pkgs/tools/text/dos2unix/default.nix

···
     changelog = "https://sourceforge.net/p/dos2unix/dos2unix/ci/dos2unix-${version}/tree/dos2unix/NEWS.txt?format=raw";
     license = licenses.bsd2;
     maintainers = with maintainers; [ c0bw3b ];
+    platforms = platforms.all;
   };
 }