Use Rubocop 0.57

Author: DirtyF

jekyll-redirect-from.gemspec

@@ -27,5 +27,5 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "jekyll-sitemap", "~> 1.0"
   spec.add_development_dependency "rake", "~> 12.0"
   spec.add_development_dependency "rspec", "~> 3.5"
-  spec.add_development_dependency "rubocop", "0.51"
+  spec.add_development_dependency "rubocop", "~> 0.57"
 end