bundle exec jekyll serve

# Gemfile
gem "github-pages"
# Gemfile.lock:
    github-pages (209)
      jekyll (= 3.9.0)
…

bundler: failed to load command: jekyll (/usr/local/lib/ruby/gems/3.0.0/bin/jekyll)
/usr/local/lib/ruby/gems/3.0.0/gems/jekyll-3.9.0/lib/jekyll/commands/serve/servlet.rb:3:in `require': cannot load such file -- webrick (LoadError)
	from /usr/local/lib/ruby/gems/3.0.0/gems/jekyll-3.9.0/lib/jekyll/commands/serve/servlet.rb:3:in `<top (required)>'
	from /usr/local/lib/ruby/gems/3.0.0/gems/jekyll-3.9.0/lib/jekyll/commands/serve.rb:184:in `require_relative'
	from /usr/local/lib/ruby/gems/3.0.0/gems/jekyll-3.9.0/lib/jekyll/commands/serve.rb:184:in `setup'
	from /usr/local/lib/ruby/gems/3.0.0/gems/jekyll-3.9.0/lib/jekyll/commands/serve.rb:102:in `process'
	from /usr/local/lib/ruby/gems/3.0.0/gems/jekyll-3.9.0/lib/jekyll/commands/serve.rb:93:in `block in start'
	from /usr/local/lib/ruby/gems/3.0.0/gems/jekyll-3.9.0/lib/jekyll/commands/serve.rb:93:in `each'
	from /usr/local/lib/ruby/gems/3.0.0/gems/jekyll-3.9.0/lib/jekyll/commands/serve.rb:93:in `start'
	from /usr/local/lib/ruby/gems/3.0.0/gems/jekyll-3.9.0/lib/jekyll/commands/serve.rb:75:in `block (2 levels) in init_with_program'
	from /usr/local/lib/ruby/gems/3.0.0/gems/mercenary-0.3.6/lib/mercenary/command.rb:220:in `block in execute'
	from /usr/local/lib/ruby/gems/3.0.0/gems/mercenary-0.3.6/lib/mercenary/command.rb:220:in `each'
	from /usr/local/lib/ruby/gems/3.0.0/gems/mercenary-0.3.6/lib/mercenary/command.rb:220:in `execute'
	from /usr/local/lib/ruby/gems/3.0.0/gems/mercenary-0.3.6/lib/mercenary/program.rb:42:in `go'
	from /usr/local/lib/ruby/gems/3.0.0/gems/mercenary-0.3.6/lib/mercenary.rb:19:in `program'
	from /usr/local/lib/ruby/gems/3.0.0/gems/jekyll-3.9.0/exe/jekyll:15:in `<top (required)>'
	from /usr/local/lib/ruby/gems/3.0.0/bin/jekyll:23:in `load'
	from /usr/local/lib/ruby/gems/3.0.0/bin/jekyll:23:in `<top (required)>'
	from /usr/local/Cellar/ruby/3.0.0_1/lib/ruby/3.0.0/bundler/cli/exec.rb:63:in `load'
	from /usr/local/Cellar/ruby/3.0.0_1/lib/ruby/3.0.0/bundler/cli/exec.rb:63:in `kernel_load'
	from /usr/local/Cellar/ruby/3.0.0_1/lib/ruby/3.0.0/bundler/cli/exec.rb:28:in `run'
	from /usr/local/Cellar/ruby/3.0.0_1/lib/ruby/3.0.0/bundler/cli.rb:497:in `exec'
	from /usr/local/Cellar/ruby/3.0.0_1/lib/ruby/3.0.0/bundler/vendor/thor/lib/thor/command.rb:27:in `run'
	from /usr/local/Cellar/ruby/3.0.0_1/lib/ruby/3.0.0/bundler/vendor/thor/lib/thor/invocation.rb:127:in `invoke_command'
	from /usr/local/Cellar/ruby/3.0.0_1/lib/ruby/3.0.0/bundler/vendor/thor/lib/thor.rb:392:in `dispatch'
	from /usr/local/Cellar/ruby/3.0.0_1/lib/ruby/3.0.0/bundler/cli.rb:30:in `dispatch'
	from /usr/local/Cellar/ruby/3.0.0_1/lib/ruby/3.0.0/bundler/vendor/thor/lib/thor/base.rb:485:in `start'
	from /usr/local/Cellar/ruby/3.0.0_1/lib/ruby/3.0.0/bundler/cli.rb:24:in `start'
	from /usr/local/Cellar/ruby/3.0.0_1/lib/ruby/gems/3.0.0/gems/bundler-2.2.3/exe/bundle:49:in `block in <top (required)>'
	from /usr/local/Cellar/ruby/3.0.0_1/lib/ruby/3.0.0/bundler/friendly_errors.rb:130:in `with_friendly_errors'
	from /usr/local/Cellar/ruby/3.0.0_1/lib/ruby/gems/3.0.0/gems/bundler-2.2.3/exe/bundle:37:in `<top (required)>'
	from /usr/local/lib/ruby/gems/3.0.0/bin/bundle:23:in `load'
	from /usr/local/lib/ruby/gems/3.0.0/bin/bundle:23:in `<main>'