Modernize dependencies

Author: hellcp

Gemfile

@@ -1,9 +1,5 @@
 source 'https://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 'github-pages'
 gem 'jekyll-paginate'
-gem 'jemoji'
+gem 'jemoji'