Bump rubocop from 0.90.0 to 0.91.0 (#14835)

Bumps [rubocop](https://github.com/rubocop-hq/rubocop) from 0.90.0 to 0.91.0.
- [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/v0.90.0...v0.91.0)

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

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

Gemfile

@@ -140,7 +140,7 @@ group :development do
   gem 'letter_opener', '~> 1.7'
   gem 'letter_opener_web', '~> 1.4'
   gem 'memory_profiler'
-  gem 'rubocop', '~> 0.90', require: false
+  gem 'rubocop', '~> 0.91', require: false
   gem 'rubocop-rails', '~> 2.8', require: false
   gem 'brakeman', '~> 4.9', require: false
   gem 'bundler-audit', '~> 0.7', require: false

Gemfile.lock

@@ -534,13 +534,13 @@ GEM
     rspec-support (3.9.3)
     rspec_junit_formatter (0.4.1)
       rspec-core (>= 2, < 4, != 2.12.0)
-    rubocop (0.90.0)
+    rubocop (0.91.0)
       parallel (~> 1.10)
       parser (>= 2.7.1.1)
       rainbow (>= 2.2.2, < 4.0)
       regexp_parser (>= 1.7)
       rexml
-      rubocop-ast (>= 0.3.0, < 1.0)
+      rubocop-ast (>= 0.4.0, < 1.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 1.4.0, < 2.0)
     rubocop-ast (0.4.2)
@@ -776,7 +776,7 @@ DEPENDENCIES
   rspec-rails (~> 4.0)
   rspec-sidekiq (~> 3.1)
   rspec_junit_formatter (~> 0.4)
-  rubocop (~> 0.90)
+  rubocop (~> 0.91)
   rubocop-rails (~> 2.8)
   ruby-progressbar (~> 1.10)
   sanitize (~> 5.2)