Bump rubocop-rails from 2.14.2 to 2.15.0

Bumps [rubocop-rails](https://github.com/rubocop/rubocop-rails) from 2.14.2 to 2.15.0.
- [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/v2.14.2...v2.15.0)

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

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

Gemfile.lock

@@ -187,7 +187,7 @@ GEM
     rainbow (3.1.1)
     rake (13.0.6)
     redis (4.6.0)
-    regexp_parser (2.4.0)
+    regexp_parser (2.5.0)
     reline (0.3.1)
       io-console (~> 0.5)
     rexml (3.2.5)
@@ -208,18 +208,18 @@ GEM
       rspec-mocks (~> 3.10)
       rspec-support (~> 3.10)
     rspec-support (3.11.0)
-    rubocop (1.29.1)
+    rubocop (1.30.1)
       parallel (~> 1.10)
       parser (>= 3.1.0.0)
       rainbow (>= 2.2.2, < 4.0)
       regexp_parser (>= 1.8, < 3.0)
       rexml (>= 3.2.5, < 4.0)
-      rubocop-ast (>= 1.17.0, < 2.0)
+      rubocop-ast (>= 1.18.0, < 2.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 1.4.0, < 3.0)
     rubocop-ast (1.18.0)
       parser (>= 3.1.1.0)
-    rubocop-rails (2.14.2)
+    rubocop-rails (2.15.0)
       activesupport (>= 4.2.0)
       rack (>= 1.1)
       rubocop (>= 1.7.0, < 2.0)