Bump rubocop-rails from 2.6.0 to 2.9.1

Bumps [rubocop-rails](https://github.com/rubocop-hq/rubocop-rails) from 2.6.0 to 2.9.1.
- [Release notes](https://github.com/rubocop-hq/rubocop-rails/releases)
- [Changelog](https://github.com/rubocop-hq/rubocop-rails/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rubocop-hq/rubocop-rails/compare/v2.6.0...v2.9.1)

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

.rubocop.yml

@@ -292,7 +292,7 @@ Rails/SaveBang:
 
 Rails/SkipsModelValidations:
   Enabled: true
-  Blacklist:
+  ForbiddenMethods:
     - update_attribute
   Exclude:
     - lib/acts_as_paranoid_aliases.rb

Gemfile

@@ -109,7 +109,7 @@ group :development do
   gem "pronto-scss", "~> 0.11.0", require: false
   gem "rubocop", "~> 0.91.0", require: false
   gem "rubocop-performance", "~> 1.7.1", require: false
-  gem "rubocop-rails", "~> 2.6.0", require: false
+  gem "rubocop-rails", "~> 2.9.1", require: false
   gem "rubocop-rspec", "~> 1.44.1", require: false
   gem "rvm1-capistrano3", "~> 1.4.0", require: false
   gem "scss_lint", "~> 0.59.0", require: false

Gemfile.lock

@@ -555,10 +555,10 @@ GEM
       parser (>= 2.7.1.5)
     rubocop-performance (1.7.1)
       rubocop (>= 0.82.0)
-    rubocop-rails (2.6.0)
+    rubocop-rails (2.9.1)
       activesupport (>= 4.2.0)
       rack (>= 1.1)
-      rubocop (>= 0.82.0)
+      rubocop (>= 0.90.0, < 2.0)
     rubocop-rspec (1.44.1)
       rubocop (~> 0.87)
       rubocop-ast (>= 0.7.1)
@@ -772,7 +772,7 @@ DEPENDENCIES
   rspec-rails (~> 4.0)
   rubocop (~> 0.91.0)
   rubocop-performance (~> 1.7.1)
-  rubocop-rails (~> 2.6.0)
+  rubocop-rails (~> 2.9.1)
   rubocop-rspec (~> 1.44.1)
   rvm1-capistrano3 (~> 1.4.0)
   sassc-rails (~> 2.1.2)