removing "/api" prefix

My config:

```
Apipie.configure do |config|
  config.app_name = "MyApp"
  config.doc_base_url = "/apipie"
  config.api_controllers_matcher = "#{Rails.root}/app/controllers/**/*.rb"
  config.validate = false
end
```

But at http://localhost:3000/apipie it still  shows the urls with "/api" prefix. 