title: Error installing json using gem. Failed to build gem native extension
body: <p>I am trying to install rails and I am receiving the following error:</p>
  
  <pre><code>ERROR:  Error installing json:
  ERROR: Failed to build gem native extension.
  
  /usr/bin/ruby2.2 -r ./siteconf20150420-9274-14pi84x.rb extconf.rb
  mkmf.rb can't find header files for ruby at /usr/lib/ruby/include/ruby.h
  
  extconf failed, exit code 1
  
  Gem files will remain installed in /var/lib/gems/2.2.0/gems/json-1.8.2 for inspection.
  Results logged to /var/lib/gems/2.2.0/extensions/x86_64-linux/2.2.0/json-1.8.2/gem_make.out
  </code></pre>
  
  <p>I have seen similar questions asked and answered but non seem to solve my problem</p>