rubocop noise: fixes FrozenStringLiteralComment

Adding the .ruby-verison file triggered previously un-run cops, specifically:

  This cop is designed to help upgrade to Ruby 3.0. It will add the
  comment `# frozen_string_literal: true` to the top of files to enable
  frozen string literals. Frozen string literals will be default in Ruby
  3.0. The comment will be added below a shebang and encoding comment. The
  frozen string literal comment is only valid in Ruby 2.3+.

More info on rubocop [Automatic-Corrections](https://github.com/bbatsov/rubocop/wiki/Automatic-Corrections)

app/channels/application_cable/channel.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module ApplicationCable
   class Channel < ActionCable::Channel::Base
   end

app/channels/application_cable/connection.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module ApplicationCable
   class Connection < ActionCable::Connection::Base
   end

app/controllers/admin/auth_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Admin
   class AuthController < AdminController
     skip_before_action :authorize_admin

app/controllers/admin/profile_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Admin
   class ProfileController < AdminController
     def view

app/controllers/admin/question_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Admin
   class QuestionController < AdminController
     def index

app/controllers/admin/quiz_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Admin
   class QuizController < AdminController
     def index

app/controllers/admin/user_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Admin
   class UserController < AdminController
     def index

app/controllers/admin_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class AdminController < ApplicationController
   layout 'admin'
   before_action :authorize_admin

app/controllers/application_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class ApplicationController < ActionController::Base
   protect_from_forgery with: :exception
 

app/controllers/candidate_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class CandidateController < ApplicationController
   before_action :authorize_candidate, except: [:login, :validate, :live_coder]
   before_action :send_to_oops, only: [:login]

app/controllers/quiz_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class QuizController < ApplicationController
   before_action :authorize_candidate
 

app/controllers/recruiter_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class RecruiterController < ApplicationController
   before_action :authorize_recruiter, except: [:login, :auth]
 

app/controllers/review_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class ReviewController < ApplicationController
   before_action :authorize_reviewer, except: [:login, :auth]
 

app/helpers/application_helper.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module ApplicationHelper
   def experience_options val
     options_for_select([

app/jobs/application_job.rb

@@ -1,2 +1,3 @@
+# frozen_string_literal: true
 class ApplicationJob < ActiveJob::Base
 end

app/mailers/application_mailer.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class ApplicationMailer < ActionMailer::Base
   default from: ENV['default_mail_from']
   layout 'mailer'

app/mailers/candidate_mailer.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class CandidateMailer < ApplicationMailer
   def welcome candidate
     @candidate = candidate

app/mailers/recruiter_mailer.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class RecruiterMailer < ApplicationMailer
   def candidate_created candidate
     @candidate = candidate

app/mailers/reviewer_mailer.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class ReviewerMailer < ApplicationMailer
   def candidate_submission candidate
     @candidate = candidate

app/mailers/user_mailer.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class UserMailer < ApplicationMailer
   def password_reset user
     @user = user

app/models/answer.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class Answer < ApplicationRecord
   serialize :answer
 

app/models/application_record.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class ApplicationRecord < ActiveRecord::Base
   self.abstract_class = true
 

app/models/candidate.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class Candidate < ApplicationRecord
   belongs_to :quiz
   has_many :questions, -> { order("sort") }, through: :quiz

app/models/question.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class Question < ApplicationRecord
   serialize :input_options
 

app/models/quiz.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class Quiz < ApplicationRecord
   has_many :questions, -> { order(:sort) }
   has_many :candidates

app/models/user.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class User < ApplicationRecord
   has_secure_password
   has_many :candidates, foreign_key: "recruiter_id"

app/services/crypt_serializer.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'openssl'
 require 'base64'
 

app/services/skill_config.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class SkillConfig < Settingslogic
   source "#{Rails.root}/config/application.yml"
   namespace Rails.env

app/validators/answer_format_validator.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class AnswerFormatValidator < ActiveModel::EachValidator
   def validate_each(record, attribute, value)
     send(record.question.input_type, record, attribute, value)

app/validators/email_format_validator.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class EmailFormatValidator < ActiveModel::EachValidator
   def validate_each(record, attribute, value)
     # EMAIL regex test

app/validators/input_options_presence_validator.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class InputOptionsPresenceValidator < ActiveModel::EachValidator
   def validate_each(record, attribute, value)
     return true unless record.input_type =~ /radio|check/i

app/workers/candidate_quiz.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class CandidateQuiz
   attr_reader :candidate_id
 

app/workers/candidate_quiz_question.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class CandidateQuizQuestion
   attr_reader :row
 

app/workers/quiz_status.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class QuizStatus
   attr_reader :candidate
 

app/workers/reminder.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class Reminder
   def initialize
     @collection = reminder_collection