neovim: disable ruby by default

Looking at the ecosystem, I don't see many ruby plugins that would
justify having ruby enabled by default.

pkgs/applications/editors/neovim/utils.nix

@@ -90,7 +90,7 @@ let
     /* the function you would have passed to lua.withPackages */
     , extraLuaPackages ? (_: [])
     , withNodeJs ? false
-    , withRuby ? true
+    , withRuby ? false
     , vimAlias ? false
     , viAlias ? false
     , configure ? {}