Bump rubocop from 1.3.1 to 1.4.0

Bumps [rubocop](https://github.com/rubocop-hq/rubocop) from 1.3.1 to 1.4.0.
- [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/v1.3.1...v1.4.0)

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

Gemfile.lock

@@ -208,7 +208,7 @@ GEM
       rack (>= 1.2, < 3)
     pagedown-bootstrap-rails (2.1.4)
       railties (> 3.1)
-    parallel (1.20.0)
+    parallel (1.20.1)
     parser (2.7.2.0)
       ast (~> 2.4.1)
     path_expander (1.1.0)
@@ -311,7 +311,7 @@ GEM
       rspec-mocks (~> 3.9)
       rspec-support (~> 3.9)
     rspec-support (3.9.4)
-    rubocop (1.3.1)
+    rubocop (1.4.0)
       parallel (~> 1.10)
       parser (>= 2.7.1.5)
       rainbow (>= 2.2.2, < 4.0)