mkmf.rb can't find header files for ruby (Error while trying to install i2cssh)

mac osx 10.14

% sudo gem install i2cssh (git)-[master]
Password:
Sorry, try again.
Password:
ERROR: Error installing i2cssh:
 ERROR: Failed to build gem native extension.

 current directory: /Library/Ruby/Gems/2.3.0/gems/rb-scpt-1.0.2
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/ruby -r ./siteconf20200724-91203-d1sipt.rb extconf.rb
mkmf.rb can't find header files for ruby at /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/include/ruby.h

extconf failed, exit code 1

Gem files will remain installed in /Library/Ruby/Gems/2.3.0/gems/rb-scpt-1.0.2 for inspection.
Results logged to /Library/Ruby/Gems/2.3.0/extensions/universal-darwin-18/2.3.0/rb-scpt-1.0.2/gem_make.out

% xcode-select --install

% sudo installer -pkg /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg -target /

% sudo gem install i2cssh (git)-[master]
Password:
Fetching: i2cssh-2.2.0.gem (100%)
Successfully installed i2cssh-2.2.0
Parsing documentation for i2cssh-2.2.0
Installing ri documentation for i2cssh-2.2.0
Done installing documentation for i2cssh after 1 seconds
1 gem installed