Bump rubocop-rails from 2.17.4 to 2.18.0

Bumps [rubocop-rails](https://github.com/rubocop/rubocop-rails) from 2.17.4 to 2.18.0.
- [Release notes](https://github.com/rubocop/rubocop-rails/releases)
- [Changelog](https://github.com/rubocop/rubocop-rails/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rubocop/rubocop-rails/compare/v2.17.4...v2.18.0)

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

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

Gemfile.lock

@@ -214,7 +214,7 @@ GEM
     combine_pdf (1.0.22)
       matrix
       ruby-rc4 (>= 0.1.5)
-    concurrent-ruby (1.2.0)
+    concurrent-ruby (1.2.2)
     connection_pool (2.3.0)
     crack (0.4.5)
       rexml
@@ -459,7 +459,7 @@ GEM
     parallel (1.22.1)
     paranoia (2.6.1)
       activerecord (>= 5.1, < 7.1)
-    parser (3.2.0.0)
+    parser (3.2.1.0)
       ast (~> 2.4.1)
     paypal-sdk-core (0.3.4)
       multi_json (~> 1.0)
@@ -615,9 +615,9 @@ GEM
       rubocop-ast (>= 1.24.1, < 2.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 2.4.0, < 3.0)
-    rubocop-ast (1.24.1)
-      parser (>= 3.1.1.0)
-    rubocop-rails (2.17.4)
+    rubocop-ast (1.26.0)
+      parser (>= 3.2.1.0)
+    rubocop-rails (2.18.0)
       activesupport (>= 4.2.0)
       rack (>= 1.1)
       rubocop (>= 1.33.0, < 2.0)