Specify rdoc version when Ruby version is under 2.2 on generated_app

Because of ruby/rdoc@51b03c3

Author: benoittgt

example_app_generator/generate_app.rb

@@ -22,6 +22,7 @@
   gsub_file "Gemfile", /.*debugger.*/, ''
   gsub_file "Gemfile", /.*byebug.*/, "gem 'byebug', '~> 9.0.6'"
   gsub_file "Gemfile", /.*puma.*/, ""
+  gsub_file "Gemfile", /.*rdoc.*/, "gem 'rdoc', '< 6.0.4'"
 
   if Rails::VERSION::STRING >= '5.0.0'
     append_to_file('Gemfile', "gem 'rails-controller-testing', :git => 'https://github.com/rails/rails-controller-testing'\n")
@@ -47,11 +48,6 @@
     |  gem 'mime-types', '< 3'
     |end
     |
-    |# Version 6.0.4 of rdoc requires Ruby 2.2
-    |if RUBY_VERSION < '2.2'
-    |  gem 'rdoc', '< 6.0.4'
-    |end
-    |
     |gem 'rspec-rails',
     |    :path => '#{rspec_rails_repo_path}',
     |    :groups => [:development, :test]