Fix No route matches missing required keys: [] error

Without this my application raises exception `ActionController::UrlGenerationError` with message from subject when trying to redirect  to root. I guess it's because of overlap with piggybak's `root` route.

With this change it works fine.

Other issue is that any `*_path` helper which appears in layout must be prefixed with `main_app` in order for it to work on orders or any piggybak pages .
Is there any way around this?