Bump rails to 5.2 and update rubocop

app/models/admin_user.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # ActiveAdmin console user.
 #

app/models/application_record.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class ApplicationRecord < ActiveRecord::Base
   self.abstract_class = true
 end

app/models/attendee.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # A guest or plus one.
 #

app/models/concerns/findable_with_token.rb

@@ -1,10 +1,12 @@
+# frozen_string_literal: true
+
 #
 # Make a model findable only when a secure token is provided.
 #
 module FindableWithToken
   extend ActiveSupport::Concern
 
-  ID_TOKEN_RX = /\A(\d+)-(\w+)\z/
+  ID_TOKEN_RX = /\A(\d+)-(\w+)\z/.freeze
 
   included do
     has_secure_token
@@ -15,12 +17,14 @@ module FindableWithToken
 
     def self.find_by_id_token(id_token)
       raise ActiveRecord::RecordNotFound unless id_token =~ ID_TOKEN_RX
+
       id = Regexp.last_match(1)
       token = Regexp.last_match(2)
 
       record = find(id)
       raise ActiveRecord::RecordNotFound unless
         ActiveSupport::SecurityUtils.secure_compare(record.token, token)
+
       record
     end
   end

app/models/guest.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # A primary guest.
 #
@@ -26,6 +28,7 @@ class Guest < ApplicationRecord
   def email_safe_salutation
     return 'Hello,' if
       first_name.blank? || first_name !~ /\A[\p{Word}\s'-]{1,30}\z/i
+
     "Dear #{first_name},"
   end
 

app/models/plus_one.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # An extra guest.
 #