Mac OS 10.12 (Sierra) does not have Ruby 2.1+ as of yet:

$ ruby –version ruby 2.0.0p648 (2015-12-16 revision 53162) [universal.x86_64-darwin16]

So I have a bit of trouble getting Jekyll working. Installing a few older versions got me going again:

$ sudo gem install jekyll -v 3.4.5
$ sudo gem install liquid -v 3.0.5
$ sudo gem install bundler
$ bundle install

Then I was able to run Jekyll normally.

The more correct way to address this problem though would be to use a more current version of Ruby. RVM allows for working with multiple Ruby environments. Below are the steps I followed to get the local copy of my Jekyll site running. I had to pick a directory that my user could read and write from to setup Homebrew during the installation.

$ gpg --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3 7D2BAF1CF37B13E2069D6956105BD0E739499BDB
$ curl -O https://raw.githubusercontent.com/rvm/rvm/master/binscripts/rvm-installer
$ curl -O https://raw.githubusercontent.com/rvm/rvm/master/binscripts/rvm-installer.asc
$ gpg --verify rvm-installer.asc
$ bash rvm-installer stable
$ rvm get head
$ rvm autolibs enable
$ rvm use --install 2.4.1 --create
$ rvm list
    rvm rubies
    ruby-2.4.1 [ x86_64 ]

    # Default ruby not set. Try 'rvm alias create default <ruby>'.

    # => - current
    # =* - current && default
    #  * - default

$ rvm use ruby-2.4.1
    Using ~/.rvm/gems/ruby-2.4.1
$ gem install jekyll
$ jekyll --version
    jekyll 3.5.2
$ gem install bundle

Then in the site’s project directory:

$ bundle install

I also had to modify my $PATH setting so that RVM’s bin directory was before where the system version of Jekyll was.