require 'rails' if not include_all_railties, just as 'rails/all' does

railties/lib/rails/generators/rails/app/templates/config/application.rb

@@ -3,6 +3,7 @@
 <% if include_all_railties? -%>
 require 'rails/all'
 <% else -%>
+require "rails"
 # Pick the frameworks you want:
 require "active_model/railtie"
 require "active_job/railtie"