Inconsistent public path in rake task and railtie
Inconsistent public path in rake task and railtie

I think we should use `config.paths['public'].first` in `output` method to make it consistent with `manifest_assets_path` in
[sprockets-rails/lib/railtie.rb](https://github.com/rails/sprockets-rails/blob/master/lib/sprockets/railtie.rb#L70)
envato/sprockets-rails,rails/sprockets-rails,spodlecki/sprockets-rails,eileencodes/sprockets-rails,prathamesh-sonpatki/sprockets-rails,Andreis13/sprockets-rails,github/sprockets-rails,zBMNForks/sprockets-rails,maclover7/sprockets-rails,jeremy/sprockets-rails,jordan-brough/sprockets-rails