config/boot.rb - Usando Bundler Com Rails 2.3 - https://medium.com/@pbalduino/usando-bundler-com-rails-2-3-d771f9f1d9c0

boot.rb

class Rails::Boot
  def run
    load_initializer

    Rails::Initializer.class_eval do
      def load_gems
        @bundler_loaded ||= Bundler.require :default, Rails.env
      end
    end

    Rails::Initializer.run(:set_load_path)
  end
end