Do not default to any Serializer

We will wait until 5.1 to make a decision

railties/lib/rails/generators/app_base.rb

@@ -278,10 +278,8 @@ module Rails
       end
 
       def jbuilder_gemfile_entry
-        return [] if options[:api]
-
         comment = 'Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder'
-        GemfileEntry.version('jbuilder', '~> 2.0', comment)
+        GemfileEntry.new 'jbuilder', '~> 2.0', comment, {}, options[:api]
       end
 
       def coffee_gemfile_entry

railties/lib/rails/generators/rails/app/templates/Gemfile

@@ -22,9 +22,6 @@ source 'https://rubygems.org'
 # gem 'capistrano-rails', group: :development
 
 <%- if options.api? -%>
-# Use ActiveModelSerializers to serialize JSON responses
-gem 'active_model_serializers', '~> 0.10.0.rc2'
-
 # Use Rack CORS for handling Cross-Origin Resource Sharing (CORS), making cross-origin AJAX possible
 # gem 'rack-cors'
 

railties/test/generators/api_app_generator_test.rb

@@ -37,9 +37,8 @@ class ApiAppGeneratorTest < Rails::Generators::TestCase
       assert_no_match(/gem 'coffee-rails'/, content)
       assert_no_match(/gem 'jquery-rails'/, content)
       assert_no_match(/gem 'sass-rails'/, content)
-      assert_no_match(/gem 'jbuilder'/, content)
       assert_no_match(/gem 'web-console'/, content)
-      assert_match(/gem 'active_model_serializers'/, content)
+      assert_match(/# gem 'jbuilder'/, content)
     end
 
     assert_file "config/application.rb" do |content|