bundlerEnv: fix documentation argument

This was ignored before.  Now that it's passed through, it's possible
to do

    (bundlerEnv {
      name = "...";
      gemdir = ./.;
      document = [ "ri" ];
    }).env

and get an environment where ri can be used to read gem documentation.

pkgs/development/ruby-modules/bundled-common/default.nix

@@ -38,7 +38,7 @@ let
   filteredGemset = filterGemset { inherit ruby groups; } importedGemset;
 
   configuredGemset = lib.flip lib.mapAttrs filteredGemset (name: attrs:
-    applyGemConfigs (attrs // { inherit ruby; gemName = name; })
+    applyGemConfigs (attrs // { inherit ruby document; gemName = name; })
   );
 
   hasBundler = builtins.hasAttr "bundler" filteredGemset;