For whatever reason, Mint 17.3 includes a really old version of ruby, where git jekyll requires at least version 2.0. Following this post you can load up a PPA with a more modern ruby.

sudo apt-get install software-properties-common
sudo apt-add-repository ppa:brightbox/ruby-ng
sudo apt-get update
sudo apt-get install ruby2.2 ruby2.2-dev
 
ruby -v
# Output: ruby 2.2.4p230 (2015-12-16 revision 53155) [x86_64-linux-gnu]

I also had to install the following packages.

sudo apt-get install zlib1g-dev nodejs
sudo gem install bundler

Now, following the github guide you can get things going.

echo "source 'https://rubygems.org'
gem 'github-pages', group: :jekyll_plugins" > Gemfile
bundle install
bundle exec jekyll new . --force

Be sure to actually follow the guide, as this is just my notes after completing install.