upgraded rubocop to 0.57.2; added two cop configuration changes to .rubocop.yml

Author: James Luberda

.rubocop.yml

@@ -17,3 +17,11 @@ Metrics/PerceivedComplexity:
 
 Style/FrozenStringLiteralComment:
   Enabled: false
+
+Naming/MemoizedInstanceVariableName:
+  Exclude:
+    - lib/jekyll-admin/page_without_a_file.rb
+
+Naming/UncommunicativeMethodParamName:
+  Exclude:
+    - lib/jekyll-admin/data_file.rb

jekyll-admin.gemspec

@@ -35,7 +35,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "bundler", "~> 1.7"
   spec.add_development_dependency "rake", "~> 10.0"
   spec.add_development_dependency "rspec", "~> 3.4"
-  spec.add_development_dependency "rubocop", "~> 0.48.1"
+  spec.add_development_dependency "rubocop", "~> 0.57.2"
   spec.add_development_dependency "sinatra-cross_origin", "~> 0.3"
   spec.add_development_dependency "gem-release", "~> 0.7"
 end