Bump rails to 5.2 and update rubocop

test/application_system_test_case.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class ApplicationSystemTestCase < ActionDispatch::SystemTestCase

test/controllers/guests_controller_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class GuestsControllerTest < ActionDispatch::IntegrationTest

test/controllers/plus_ones_controller_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class PlusOnesControllerTest < ActionDispatch::IntegrationTest

test/controllers/welcome_controller_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class WelcomeControllerTest < ActionDispatch::IntegrationTest

test/mailers/guest_mailer_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class GuestMailerTest < ActionMailer::TestCase

test/mailers/previews/guest_mailer_preview.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Preview all emails at http://localhost:3000/rails/mailers/guest_mailer
 class GuestMailerPreview < ActionMailer::Preview
   def confirmation_email_attending

test/models/admin_user_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class AdminUserTest < ActiveSupport::TestCase

test/models/attendee_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class AttendeeTest < ActiveSupport::TestCase

test/models/guest_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class GuestTest < ActiveSupport::TestCase

test/models/plus_one_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class PlusOneTest < ActiveSupport::TestCase

test/system/rsvp_happy_path_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'application_system_test_case'
 
 class RsvpHappyPathTest < ApplicationSystemTestCase

test/test_helper.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 ENV['RAILS_ENV'] ||= 'test'
 require File.expand_path('../config/environment', __dir__)
 require 'rails/test_help'