title: Terminal error message when trying to install Sass
body: <p>Below is the exact message returned from terminal:</p>
  
  <blockquote>
    <p>ERROR: Error installing sass:
           ERROR failed to build gem native extension.
           current directory: /Library/Ruby/Gems/2.0.0/gems/ffi-1.9.18/ext/ffi_c
    /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby -r
    ./siteconf20170721-3751-3vsh43.rb extconf.rb mkmf.rb can't find header
    files for ruby at
    /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/include/ruby.h</p>
    
    <p>extconf failed, exit code 1</p>
    
    <p>Gem files will remain installed in
    /Library/Ruby/Gems/2.0.0/gems/ffi-1.9.18 for inspection. Results
    logged to
    /Library/Ruby/Gems/2.0.0/extensions/universal-darwin-16/2.0.0/ffi-1.9.18/gem_make.out</p>
  </blockquote>
  
  <p>I tried both options, including <code>gem install sass</code> and <code>sudo gem install sass</code>. @Carnaru Valentin said to try <code>sudo apt-get install ruby2.1-dev build-essential</code>. When I tried this, terminal returned <code>sudo: apt-get: command not found</code>. I am running macOS. Anyone know how to solve this issue?</p>