title: Ruby bundle install error with json-1.7.3
body: <p>I am getting following error while installing ruby gems. I am using Ubuntu</p>
  
  <pre><code>Installing json (1.7.3) with native extensions
  Gem::Installer::ExtensionBuildError: 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 `&lt;main&gt;'
  
  
  Gem files will remain installed in /var/lib/gems/1.9.1/gems/json-1.7.3 for inspection.
  Results logged to /var/lib/gems/1.9.1/gems/json-1.7.3/ext/json/ext/parser/gem_make.out
  An error occured while installing json (1.7.3), and Bundler cannot continue.
  Make sure that `gem install json -v '1.7.3'` succeeds before bundling.
  </code></pre>
  
  <p>I just saw this link, and not sure what to do with devkit*.exe files on ubuntu.</p>