Update rubocop-rails to version 2.21.0

Gemfile.lock

@@ -32,6 +32,7 @@ GEM
       tzinfo (~> 2.0)
     amq-protocol (2.3.2)
     ast (2.4.2)
+    base64 (0.1.1)
     bootsnap (1.16.0)
       msgpack (~> 1.2)
     builder (3.2.4)
@@ -84,7 +85,7 @@ GEM
     lumberjack (1.2.8)
     method_source (1.0.0)
     mini_portile2 (2.8.2)
-    minitest (5.18.1)
+    minitest (5.20.0)
     msgpack (1.5.2)
     multi_json (1.15.0)
     mysql2 (0.5.5)
@@ -103,7 +104,7 @@ GEM
       coderay (~> 1.1)
       method_source (~> 1.0)
     racc (1.7.1)
-    rack (2.2.7)
+    rack (2.2.8)
     rack-test (2.1.0)
       rack (>= 1.3)
     rails-dom-testing (2.1.1)
@@ -149,7 +150,8 @@ GEM
       rspec-mocks (~> 3.12)
       rspec-support (~> 3.12)
     rspec-support (3.12.0)
-    rubocop (1.55.1)
+    rubocop (1.56.2)
+      base64 (~> 0.1.1)
       json (~> 2.3)
       language_server-protocol (>= 3.17.0)
       parallel (~> 1.10)
@@ -169,7 +171,7 @@ GEM
     rubocop-performance (1.18.0)
       rubocop (>= 1.7.0, < 2.0)
       rubocop-ast (>= 0.4.0)
-    rubocop-rails (2.20.2)
+    rubocop-rails (2.21.0)
       activesupport (>= 4.2.0)
       rack (>= 1.1)
       rubocop (>= 1.33.0, < 2.0)