docs/_docs/upgrading.md
Upgrading from an older version of Jekyll? Upgrading to a new major version of Jekyll (e.g. from v2.x to v3.x) may cause some headaches. Take the following guides to aid your upgrade:
If you followed our setup recommendations and installed Bundler, run bundle update jekyll or simply bundle update and all your gems will
update to the latest versions.
If you don't have Bundler installed, run gem update jekyll.
The procedure is similar if you use the github-pages
gem.