Bundle update with native extensions fails

Bundle update with native extensions fails

$ xcode-select --install

If it still fails:

$ cd /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/include/ruby-2.6.0/ruby
$ ln -sf ../../../../Headers/ruby/config.h

$ cd /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/include/ruby-2.6.0
$ ln -sf universal-darwin20 universal-darwin19

Bundle update downgrades github-pages

solution for https://github.com/bundler/bundler/issues/5154

gem 'github-pages', '104', group: :jekyll_plugins

cannot load such file – webrick (LoadError)

https://github.com/jekyll/jekyll/issues/8523

gem "webrick"