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 are making a minor update (for example from 3.3.1 to the latest version at the time 3.3.2) run ‘bundle update jekyll’ when in your site directory. If you would like to update all your gems, run ‘bundle update’ when in your site directory.