Bump rubocop-rails from 2.20.2 to 2.21.0

Bumps [rubocop-rails](https://github.com/rubocop/rubocop-rails) from 2.20.2 to 2.21.0.
- [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...v2.21.0)

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

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

Gemfile.lock

@@ -91,6 +91,7 @@ GEM
       aws-sigv4 (~> 1.6)
     aws-sigv4 (1.6.0)
       aws-eventstream (~> 1, >= 1.0.2)
+    base64 (0.1.1)
     bcrypt (3.1.19)
     bootsnap (1.16.0)
       msgpack (~> 1.2)
@@ -174,7 +175,7 @@ GEM
     method_source (1.0.0)
     mini_magick (4.12.0)
     mini_mime (1.1.2)
-    minitest (5.19.0)
+    minitest (5.20.0)
     mocha (2.1.0)
       ruby2_keywords (>= 0.0.5)
     msgpack (1.7.2)
@@ -248,7 +249,8 @@ GEM
     reline (0.3.7)
       io-console (~> 0.5)
     rexml (3.2.6)
-    rubocop (1.55.1)
+    rubocop (1.56.2)
+      base64 (~> 0.1.1)
       json (~> 2.3)
       language_server-protocol (>= 3.17.0)
       parallel (~> 1.10)
@@ -265,7 +267,7 @@ GEM
       rubocop (~> 1.41)
     rubocop-factory_bot (2.23.1)
       rubocop (~> 1.33)
-    rubocop-rails (2.20.2)
+    rubocop-rails (2.21.0)
       activesupport (>= 4.2.0)
       rack (>= 1.1)
       rubocop (>= 1.33.0, < 2.0)