Update from Rails 5.1.6 to Rails 5.2.0

① Changed description in Gemfile to rails 5.2.0

② bundle update

③ rails app:update

④ Since rails 5.2.0 requires gem called bootsnap, it is added to Gemfile
　gem 'bootsnap'

⑤ bundle install

⑥
$ pwd
/var/www/rails/rails5/config/initializers
$ vim callback_terminator.rb
#ActiveSupport.halt_callback_chains_on_return_false = false

⑥ rails s