Set BUNDLE_WITHOUT to install less dependencies

Author: toshimaru

Rakefile

@@ -46,6 +46,9 @@ end
 def generate_rails_rdoc
   cd 'rails' do
     Bundler.with_unbundled_env do
+      # TODO: use `BUNDLE_ONLY`(require bundler 2.3.19+).
+      ENV['BUNDLE_WITHOUT'] = 'db:job:storage'
+
       # replace sdoc gem
       gemfile = File.read('Gemfile')
       gemfile.gsub!(/"sdoc.*$/, '"sdoc", github: "toshimaru/sdoc", branch: "railsdoc"')