Switch to use github-pages gem

Gemfile

@@ -8,16 +8,21 @@ source 'https://rubygems.org'
 #
 # This will help ensure the proper Jekyll version is running.
 # Happy Jekylling!
-gem 'jekyll', '3.5.0'
+# gem 'jekyll', '3.5.0'
 
 # If you want to use GitHub Pages, remove the "gem "jekyll"" above and
 # uncomment the line below. To upgrade, run `bundle update github-pages`.
-# gem "github-pages", group: :jekyll_plugins
+gem 'github-pages', group: :jekyll_plugins
+
+group :development do
+  gem 'rake'
+  gem 'rubocop'
+end
 
 # If you have any plugins, put them here!
 group :jekyll_plugins do
-  gem 'jekyll-sitemap'
   gem 'jekyll-seo-tag'
+  gem 'jekyll-sitemap'
 end
 
 # Windows does not include zoneinfo files, so bundle the tzinfo-data gem