Bump rubocop from 0.83.0 to 0.84.0 (#13843)

Bumps [rubocop](https://github.com/rubocop-hq/rubocop) from 0.83.0 to 0.84.0.
- [Release notes](https://github.com/rubocop-hq/rubocop/releases)
- [Changelog](https://github.com/rubocop-hq/rubocop/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rubocop-hq/rubocop/compare/v0.83.0...v0.84.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Gemfile

@@ -139,7 +139,7 @@ group :development do
   gem 'letter_opener', '~> 1.7'
   gem 'letter_opener_web', '~> 1.4'
   gem 'memory_profiler'
-  gem 'rubocop', '~> 0.83', require: false
+  gem 'rubocop', '~> 0.84', require: false
   gem 'rubocop-rails', '~> 2.5', require: false
   gem 'brakeman', '~> 4.8', require: false
   gem 'bundler-audit', '~> 0.6', require: false

Gemfile.lock

@@ -543,13 +543,16 @@ GEM
     rspec-support (3.9.3)
     rspec_junit_formatter (0.4.1)
       rspec-core (>= 2, < 4, != 2.12.0)
-    rubocop (0.83.0)
+    rubocop (0.84.0)
       parallel (~> 1.10)
       parser (>= 2.7.0.1)
       rainbow (>= 2.2.2, < 4.0)
       rexml
+      rubocop-ast (>= 0.0.3)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 1.4.0, < 2.0)
+    rubocop-ast (0.0.3)
+      parser (>= 2.7.0.1)
     rubocop-rails (2.5.2)
       activesupport
       rack (>= 1.1)
@@ -768,7 +771,7 @@ DEPENDENCIES
   rspec-rails (~> 4.0)
   rspec-sidekiq (~> 3.0)
   rspec_junit_formatter (~> 0.4)
-  rubocop (~> 0.83)
+  rubocop (~> 0.84)
   rubocop-rails (~> 2.5)
   ruby-progressbar (~> 1.10)
   sanitize (~> 5.1)