Summary

I tried rebuilding today after 7 months of forgetting how this works and when I tried to jekyll build I got

$ jekyll build
Traceback (most recent call last):
...
/usr/local/Cellar/ruby/2.6.5/lib/ruby/2.6.0/bundler/lockfile_parser.rb:108:in `warn_for_outdated_bundler_version': You must use Bundler 2 or greater with this lockfile. (Bundler::LockfileError)

Per this answer, I ran gem list bundler to see my rubygems version and then gem update --system

$ gem list bundler

*** LOCAL GEMS ***

bundler (2.0.2, 1.17.2)
$ gem update --system
Updating rubygems-update
Fetching rubygems-update-3.1.3.gem
Successfully installed rubygems-update-3.1.3
...
...
RubyGems installed the following executables:
	/usr/local/Cellar/ruby/2.6.5/bin/gem
	/usr/local/Cellar/ruby/2.6.5/bin/bundle
    
RubyGems system software updated
  • Now I get
$ gem list bundler

*** LOCAL GEMS ***

bundler (default: 2.1.4, 2.0.2, 1.17.2)
$ 
  • And now my jekyll build worked!