Upgrade: Bump rubocop-rails from 2.20.2 to 2.21.1

Bumps [rubocop-rails](https://github.com/rubocop/rubocop-rails) from 2.20.2 to 2.21.1.
- [Release notes](https://github.com/rubocop/rubocop-rails/releases)
- [Changelog](https://github.com/rubocop/rubocop-rails/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop-rails@v2.20.2...v2.21.1)

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

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile

@@ -51,7 +51,7 @@ group :development do
   gem 'rack-mini-profiler'
   gem 'rubocop', '~> 1.56', require: false
   gem 'rubocop-performance', '~> 1.19', require: false
-  gem 'rubocop-rails', '~> 2.20', require: false
+  gem 'rubocop-rails', '~> 2.21', require: false
   gem 'rubocop-rspec', '~> 2.23', require: false
   gem 'web-console', '~> 4.2'
 end

Gemfile.lock

@@ -467,7 +467,7 @@ GEM
     rubocop-performance (1.19.0)
       rubocop (>= 1.7.0, < 2.0)
       rubocop-ast (>= 0.4.0)
-    rubocop-rails (2.20.2)
+    rubocop-rails (2.21.1)
       activesupport (>= 4.2.0)
       rack (>= 1.1)
       rubocop (>= 1.33.0, < 2.0)
@@ -628,7 +628,7 @@ DEPENDENCIES
   rspec_junit_formatter (~> 0.6)
   rubocop (~> 1.56)
   rubocop-performance (~> 1.19)
-  rubocop-rails (~> 2.20)
+  rubocop-rails (~> 2.21)
   rubocop-rspec (~> 2.23)
   ruby-progressbar (~> 1.13)
   sass-rails (~> 6.0)