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)

config/application.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'boot'
 
 require 'rails/all'

config/boot.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../Gemfile', __dir__)
 
 require 'bundler/setup' # Set up gems listed in the Gemfile.

config/environment.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Load the Rails application.
 require_relative 'application'
 

config/environments/development.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 Rails.application.configure do
   # Settings specified here will take precedence over those in config/application.rb.
 

config/environments/production.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 Rails.application.configure do
   # Settings specified here will take precedence over those in config/application.rb.
 

config/environments/test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 Rails.application.configure do
   # Settings specified here will take precedence over those in config/application.rb.
 

config/initializers/application_controller_renderer.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Be sure to restart your server when you modify this file.
 
 # ApplicationController.renderer.defaults.merge!(

config/initializers/assets.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Be sure to restart your server when you modify this file.
 
 # Version of your assets, change this if you want to expire all your assets.

config/initializers/backtrace_silencers.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Be sure to restart your server when you modify this file.
 
 # You can add backtrace silencers for libraries that you're using but don't wish to see in your backtraces.

config/initializers/cookies_serializer.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Be sure to restart your server when you modify this file.
 
 # Specify a serializer for the signed and encrypted cookie jars.

config/initializers/custom_error_wrapper.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # TODO: needs better wrapping instead of nuking
 # https://rubyplus.com/articles/3401
 ActionView::Base.field_error_proc = proc do |html_tag, _instance|

config/initializers/filter_parameter_logging.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Be sure to restart your server when you modify this file.
 
 # Configure sensitive parameters which will be filtered from the log file.

config/initializers/inflections.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Be sure to restart your server when you modify this file.
 
 # Add new inflection rules using the following format. Inflections

config/initializers/mailjet.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 Mailjet.configure do |config|
   config.api_key = ENV['mailjet_key']
   config.secret_key = ENV['mailjet_secret']

config/initializers/mime_types.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Be sure to restart your server when you modify this file.
 
 # Add new mime types for use in respond_to blocks:

config/initializers/new_framework_defaults.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Be sure to restart your server when you modify this file.
 #
 # This file contains migration options to ease your Rails 5.0 upgrade.

config/initializers/session_store.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Be sure to restart your server when you modify this file.
 
 Rails.application.config.session_store :cookie_store, key: '_skill-assessment-app_session'

config/initializers/wrap_parameters.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Be sure to restart your server when you modify this file.
 
 # This file contains settings for ActionController::ParamsWrapper which

config/puma.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Puma can serve each request in a thread from an internal thread pool.
 # The `threads` method setting takes two numbers a minimum and maximum.
 # Any libraries that use thread pools should be configured to match

config/routes.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 Rails.application.routes.draw do
   post "/admin/login",              to: "admin/auth#auth",           as: :admin_auth
   get  "/admin/login",              to: "admin/auth#login",          as: :admin_login

config/spring.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 %w(
   .ruby-version
   .rbenv-vars