Bump rubocop-rails from 2.19.1 to 2.20.0

Bumps [rubocop-rails](https://github.com/rubocop/rubocop-rails) from 2.19.1 to 2.20.0.
- [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/v2.19.1...v2.20.0)

---
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

@@ -232,7 +232,7 @@ GEM
     mini_magick (4.12.0)
     mini_mime (1.1.2)
     mini_portile2 (2.8.2)
-    minitest (5.18.0)
+    minitest (5.18.1)
     mnemosyne-ruby (1.13.0)
       activesupport (>= 4)
       bunny
@@ -292,7 +292,7 @@ GEM
       nio4r (~> 2.0)
     pundit (2.3.0)
       activesupport (>= 3.0.0)
-    racc (1.7.0)
+    racc (1.7.1)
     rack (2.2.7)
     rack-mini-profiler (3.1.0)
       rack (>= 1.2.0)
@@ -400,7 +400,7 @@ GEM
     rubocop-performance (1.18.0)
       rubocop (>= 1.7.0, < 2.0)
       rubocop-ast (>= 0.4.0)
-    rubocop-rails (2.19.1)
+    rubocop-rails (2.20.0)
       activesupport (>= 4.2.0)
       rack (>= 1.1)
       rubocop (>= 1.33.0, < 2.0)