Fix rubocop issues

app/channels/application_cable/channel.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ApplicationCable
   class Channel < ActionCable::Channel::Base
   end

app/channels/application_cable/connection.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ApplicationCable
   class Connection < ActionCable::Connection::Base
   end

app/controllers/application_controller.rb

@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 class ApplicationController < ActionController::Base
 end

app/helpers/application_helper.rb

@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 module ApplicationHelper
 end

app/jobs/application_job.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class ApplicationJob < ActiveJob::Base
   # Automatically retry jobs that encountered a deadlock
   # retry_on ActiveRecord::Deadlocked

app/mailers/application_mailer.rb

@@ -1,4 +1,6 @@
+# frozen_string_literal: true
+
 class ApplicationMailer < ActionMailer::Base
-  default from: "from@example.com"
-  layout "mailer"
+  default from: 'from@example.com'
+  layout 'mailer'
 end

app/models/application_record.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class ApplicationRecord < ActiveRecord::Base
   primary_abstract_class
 end