Error

>> bundle exec jekyll serve --trace
Traceback (most recent call last):
        2: from /usr/bin/bundle:23:in `<main>'
        1: from /Library/Ruby/Site/2.6.0/rubygems.rb:284:in `activate_bin_path'
/Library/Ruby/Site/2.6.0/rubygems.rb:265:in `find_spec_for_exe': can't find gem bundler (>= 0.a) w

Solutions

rm Gemfile.lock
bundle install