Gemfile

source "https://rubygems.org"
ruby RUBY_VERSION

# Hello! This is where you manage which Jekyll version is used to run.
# When you want to use a different version, change it below, save the
# file and run `bundle install`. Run Jekyll with `bundle exec`, like so:
#
#     bundle exec jekyll serve
#
# This will help ensure the proper Jekyll version is running.
# Happy Jekylling!
#gem "jekyll", "3.2.1"
#gem "jekyll", "3.3.1"

# This is the default theme for new Jekyll sites. You may change this to anything you like.
#gem "minima"

# 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

# If you have any plugins, put them here!
# group :jekyll_plugins do
#   gem "jekyll-github-metadata", "~> 1.0"
# end

require 'json'
require 'open-uri'
versions = JSON.parse(open('https://pages.github.com/versions.json').read)

gem 'github-pages', versions['github-pages']