gem install alfi error

[hlllmr1314]

Hi ：
$ sudo gem install alfi
Building native extensions. This could take a while...
ERROR: Error installing alfi:
ERROR: Failed to build gem native extension.

    /usr/bin/ruby1.9.1 extconf.rb

/usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in require': cannot load such file -- mkmf (LoadError) from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in require'
from extconf.rb:1:in `

'

Gem files will remain installed in /var/lib/gems/1.9.1/gems/json-2.0.3 for inspection.

[cesarferreira]

The min ruby required is 2.0.0 spec.required_ruby_version = '>= 2.0.0'

Please update your ruby (I don't know how rubygems let's you install a gem that's below the requirements)