Bump rubocop-rails from 2.11.3 to 2.15.2

Bumps [rubocop-rails](https://github.com/rubocop/rubocop-rails) from 2.11.3 to 2.15.2.
- [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/v2.11.3...v2.15.2)

---
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

@@ -108,7 +108,7 @@ group :development do
   gem "pronto-scss", "~> 0.11.0", require: false
   gem "rubocop", "~> 1.18.4", require: false
   gem "rubocop-performance", "~> 1.11.4", require: false
-  gem "rubocop-rails", "~> 2.11.3", require: false
+  gem "rubocop-rails", "~> 2.15.2", require: false
   gem "rubocop-rspec", "~> 2.4.0", require: false
   gem "rvm1-capistrano3", "~> 1.4.0", require: false
   gem "scss_lint", "~> 0.59.0", require: false

Gemfile.lock

@@ -559,7 +559,7 @@ GEM
     rubocop-performance (1.11.4)
       rubocop (>= 1.7.0, < 2.0)
       rubocop-ast (>= 0.4.0)
-    rubocop-rails (2.11.3)
+    rubocop-rails (2.15.2)
       activesupport (>= 4.2.0)
       rack (>= 1.1)
       rubocop (>= 1.7.0, < 2.0)
@@ -778,7 +778,7 @@ DEPENDENCIES
   rspec-rails (~> 5.0)
   rubocop (~> 1.18.4)
   rubocop-performance (~> 1.11.4)
-  rubocop-rails (~> 2.11.3)
+  rubocop-rails (~> 2.15.2)
   rubocop-rspec (~> 2.4.0)
   rvm1-capistrano3 (~> 1.4.0)
   sassc-rails (~> 2.1.2)