1. 更新ruby到最新版本

brew install ruby

...
ruby is keg-only, which means it was not symlinked into /usr/local,
because macOS already provides this software and installing another version in
parallel can cause all kinds of trouble.

If you need to have ruby first in your PATH, run:
  echo 'export PATH="/usr/local/opt/ruby/bin:$PATH"' >> ~/.zshrc

For compilers to find ruby you may need to set:
  export LDFLAGS="-L/usr/local/opt/ruby/lib"
  export CPPFLAGS="-I/usr/local/opt/ruby/include"

For pkg-config to find ruby you may need to set:
  export PKG_CONFIG_PATH="/usr/local/opt/ruby/lib/pkgconfig"

接下来直接使用/usr/local/opt/ruby/bin目录下的gem

1. 修改源

   /usr/local/opt/ruby/bin/gem sources --remove https://gems.ruby-china.com/
   /usr/local/opt/ruby/bin/gem sources -a https://mirrors.cloud.tencent.com/rubygems/
   

2. 安装

   /usr/local/opt/ruby/bin/gem install jekyll github-pages
   /usr/local/opt/ruby/bin/bundle add webrick
   

3. 运行

   /usr/local/opt/ruby/bin/bundle exec jekyll serve