gem install --user redcarpet pygments.rb

Hi:

After I updated macOS Catalina, Markdown Preview no longer works. I got the following error message:

Please install the Redcarpet and Pygments.rb RubyGems by running the following:

/usr/bin/gem install --user redcarpet pygments.rb

After I ran the above command, I received the following error message from the Terminal:

$ /usr/bin/gem install --user redcarpet pygments.rb

Building native extensions. This could take a while...

ERROR:  Error installing redcarpet:

ERROR: Failed to build gem native extension.

    current directory: /Users/tzha/.gem/ruby/2.6.0/gems/redcarpet-3.5.0/ext/redcarpet

/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/bin/ruby -I /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/2.6.0 -r ./siteconf20191111-836-11oqvm2.rb extconf.rb

mkmf.rb can't find header files for ruby at /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/include/ruby.h

You might have to install separate package for the ruby development

environment, ruby-dev or ruby-devel for example.

extconf failed, exit code 1

Gem files will remain installed in /Users/tzha/.gem/ruby/2.6.0/gems/redcarpet-3.5.0 for inspection.

Results logged to /Users/tzha/.gem/ruby/2.6.0/extensions/universal-darwin-19/2.6.0/redcarpet-3.5.0/gem_make.out

Successfully installed pygments.rb-1.2.1

Parsing documentation for pygments.rb-1.2.1

Done installing documentation for pygments.rb after 0 seconds

1 gem installed

Can someone help me to resolve this issue?

Thanks,

Tao