Gemfile

require "json"
require "open-uri"

source "https://rubygems.org"

versions = open("https://pages.github.com/versions.json") do |source|
  JSON.parse(source.read)
end

# Github Pages environment
gem "github-pages", versions['github-pages']
gem "redcarpet"

gem "html-proofer", '>=3.3.1', '<4.0.0'