oghliner supported plug-in for offlining Jekyll sites.
Ensure your version of Jekyll is 3.x.x and you have oghliner installed as cli:
$ npm install -g oghliner
Copy the file jekyll-offline.rb that you'll find in the repository to your _plugins folder inside your Jekyll source location. If the folder does not exist,create it first.
Add the tag {% offline_manager %} to your head.html include (or wherever you choose) to link the proper scripts.