Upgrade Rubocop to latest version (0.74)

Now that we don't need to support Ruby 2.1 or 2.2, we can use the latest
version of Rubocop (which dropped support for those versions).

Also remove things from Rubocop which are now defaults:

- FrozenStringLiteralComment is now on by default
- DisplayCopNames used to be off by default but now seems to be on
- This project doesn't seem to have ever had gemfiles or vendor
  directories - my guess is that this was a copy-paste from another
  project.

.rubocop.yml

@@ -1,9 +1,6 @@
 AllCops:
-  DisplayCopNames: true
-  TargetRubyVersion: 2.2
+  TargetRubyVersion: 2.3
   Exclude:
-    - "gemfiles/**/*"
-    - "vendor/**/*"
     - "lib/generators/**/*"
 
 Metrics/BlockLength:
@@ -46,9 +43,6 @@ Layout/AccessModifierIndentation:
 Layout/EndAlignment:
   EnforcedStyleAlignWith: variable
 
-Style/FrozenStringLiteralComment:
-  Enabled: true
-
 Style/PercentLiteralDelimiters:
   PreferredDelimiters:
     '%w': "[]"

lib/pundit.rb

@@ -15,7 +15,7 @@ class Pundit::Error < StandardError; end # rubocop:disable Style/ClassAndModuleC
 
 # @api public
 module Pundit
-  SUFFIX = "Policy".freeze
+  SUFFIX = "Policy"
 
   # @api private
   module Generators; end
@@ -124,7 +124,7 @@ module Pundit
     # @return [Object, nil] instance of policy class with query methods
     def policy(user, record)
       policy = PolicyFinder.new(record).policy
-      policy.new(user, pundit_model(record)) if policy
+      policy&.new(user, pundit_model(record))
     rescue ArgumentError
       raise InvalidConstructorError, "Invalid #<#{policy}> constructor is called"
     end

lib/pundit/version.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module Pundit
-  VERSION = "2.1.0".freeze
+  VERSION = "2.1.0"
 end

pundit.gemspec

@@ -26,6 +26,6 @@ Gem::Specification.new do |gem|
   gem.add_development_dependency "pry"
   gem.add_development_dependency "rake"
   gem.add_development_dependency "rspec", ">= 2.0.0"
-  gem.add_development_dependency "rubocop", "0.57.2"
+  gem.add_development_dependency "rubocop", "0.74.0"
   gem.add_development_dependency "yard"
 end

spec/spec_helper.rb

@@ -201,9 +201,9 @@ end
 class Controller
   include Pundit
   # Mark protected methods public so they may be called in test
-  # rubocop:disable Layout/AccessModifierIndentation, Style/AccessModifierDeclarations
+  # rubocop:disable Style/AccessModifierDeclarations
   public(*Pundit.protected_instance_methods)
-  # rubocop:enable Layout/AccessModifierIndentation, Style/AccessModifierDeclarations
+  # rubocop:enable Style/AccessModifierDeclarations
 
   attr_reader :current_user, :action_name, :params