Bump rubocop from 1.20.0 to 1.21.0 (#16733)

Bumps [rubocop](https://github.com/rubocop/rubocop) from 1.20.0 to 1.21.0.
- [Release notes](https://github.com/rubocop/rubocop/releases)
- [Changelog](https://github.com/rubocop/rubocop/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rubocop/rubocop/compare/v1.20.0...v1.21.0)

---
updated-dependencies:
- dependency-name: rubocop
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Gemfile

@@ -134,7 +134,7 @@ group :development do
   gem 'letter_opener', '~> 1.7'
   gem 'letter_opener_web', '~> 1.4'
   gem 'memory_profiler'
-  gem 'rubocop', '~> 1.20', require: false
+  gem 'rubocop', '~> 1.21', require: false
   gem 'rubocop-rails', '~> 2.11', require: false
   gem 'brakeman', '~> 5.1', require: false
   gem 'bundler-audit', '~> 0.8', require: false

Gemfile.lock

@@ -522,7 +522,7 @@ GEM
     rspec-support (3.10.2)
     rspec_junit_formatter (0.4.1)
       rspec-core (>= 2, < 4, != 2.12.0)
-    rubocop (1.20.0)
+    rubocop (1.21.0)
       parallel (~> 1.10)
       parser (>= 3.0.0.0)
       rainbow (>= 2.2.2, < 4.0)
@@ -766,7 +766,7 @@ DEPENDENCIES
   rspec-rails (~> 5.0)
   rspec-sidekiq (~> 3.1)
   rspec_junit_formatter (~> 0.4)
-  rubocop (~> 1.20)
+  rubocop (~> 1.21)
   rubocop-rails (~> 2.11)
   ruby-progressbar (~> 1.11)
   sanitize (~> 6.0)