Upgrade Rails to version 5.2.0 (#5898)

Gemfile

Gemfile.lock

app/controllers/api/web/push_subscriptions_controller.rb

app/controllers/settings/follower_domains_controller.rb

app/models/account.rb

app/models/notification.rb

app/models/status.rb

bin/bundle

bin/setup

bin/update

bin/webpack

bin/webpack-dev-server

bin/yarn

config/application.rb

config/boot.rb

config/deploy.rb

config/environments/development.rb

config/environments/production.rb

config/environments/test.rb

config/initializers/content_security_policy.rb