fix sort in lists.nix

pkgs/lib/lists.nix

@@ -190,7 +190,7 @@ rec {
         else let
           part = partition (strictLess (head l)) (tail l);
         in
-          qs part.wrong ([(head l)] ++ qs part.right []);
+          qs part.wrong ([(head l)] ++ qs part.right concat);
     in
       qs list [];
 

pkgs/lib/tests.nix

@@ -104,5 +104,10 @@ runTests {
         ];
     expected = true;
   };
+
+  testSort = {
+    expr = sort builtins.lessThan [ 40 2 30 42 ];
+    expected = [2 30 40 42];
+  };
   
 }