hanami/chat

I just upgraded our Hanami application from alpha8 to beta1. The project was setup using the Hanami 2 template. We now get this error when running rspec:

$ bundle exec rake

An error occurred while loading spec_helper.
Failure/Error: require "hanami/prepare"

NoMethodError:
  undefined method `source_dirs' for #<Hanami::Configuration:0x000000010636bad0 @config=#<Dry::Configurable::Config ... (see full stack trace in thread)
# ./config/app.rb:13:in `<class:App>'
# ./config/app.rb:6:in `<module:MyApp>'
# ./config/app.rb:5:in `<top (required)>'
# ./spec/spec_helper.rb:6:in `require'
# ./spec/spec_helper.rb:6:in `<top (required)>'

Anyone here knowing anything about this source_dirs, has it been renamed? I can't find anything in the Hanami changelog about this. This is my config/app.rb:

# frozen_string_literal: true

require "hanami"

module MyApp
  class App < Hanami::App
    config.sessions = :cookie, {
      key: "my-app.session",
      secret: settings.session_secret,
      expire_after: 60 * 60 * 24 * 365 # 1 year
    }

    config.source_dirs.component_dirs.add "serializers" # <--- crashes here
  end
end

This code worked in Hanami alpha8.