Install RVM (source):

1. Get RVM:

   sudo apt-get install software-properties-common
   sudo apt-add-repository -y ppa:rael-gc/rvm
   sudo apt-get update
   sudo apt-get install rvm
   

2. Gnome Terminal profile --> "Run command as a login shell"

3. Reboot

4. Execute:

   rvm install ruby
   gem install bundler
   bundle install
   bundle exec jekyll serve --watch --incremental