mathematica: fix sort predicate stability

Incorrect sorting predicate was found as part of
NixOS/nix#12106 where `nix` was crashing on
the code like:

    $ nix eval --expr 'builtins.sort (a: b: true) [ 1 2 3 ]'
    ...
    Aborted (core dumped)

Note: the crash happens here because sorting predicate does not
implement `lessThan` and triggers assertion failures for
`std::stable_sort` that backs `builtins.sort`.

The change restores `lessThan` semantic for version sorting.

pkgs/applications/science/math/mathematica/default.nix

@@ -30,7 +30,7 @@
 let
   versions = callPackage ./versions.nix { };
 
-  matching-versions = lib.sort (v1: v2: lib.versionAtLeast v1.version v2.version) (
+  matching-versions = lib.sort (v1: v2: lib.versionOlder v2.version v1.version) (
     lib.filter (
       v: v.lang == lang && (version == null || isMatching v.version version) && matchesDoc v
     ) versions