每次部署的时候都执行 bundle install 的话感觉很慢也好像没那么必要，所以能不能判断如果添加了新的 gem 才执行 bundle install？

如果可以怎么写这个 task？

deploy.rb

after :finishing, :bundle do
    on roles :all do
      within current_path do
        info "Current is: #{current_path}"
        execute "cd #{current_path}; bundle install --deployment --without development test"
        execute "cd #{current_path}; bundle exec rake assets:precompile RAILS_ENV=#{fetch(:stage)}"
        execute "cd #{current_path}; bundle exec rake db:migrate RAILS_ENV=#{fetch(:stage)}"
        execute "cd #{current_path}; passenger-config restart-app $(pwd)"
      end 
    end
  end