Update ruby version, Gemfile, and post CSS

Gemfile

@@ -1,7 +1,4 @@
 source 'http://rubygems.org'
 
-require 'json'
-require 'open-uri'
-versions = JSON.parse(open('https://pages.github.com/versions.json').read)
-
-gem 'github-pages', versions['github-pages']
+gem "webrick"
+gem 'github-pages', group: :jekyll_plugins