title: Gem::Ext::BuildError: ERROR: Failed to build gem native extension for rails version 4.2.6
body: <p>I have created new rails app and try to run <strong>bundle install</strong> it shows this error,</p>
  
  <pre><code>Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
  current directory: /var/lib/gems/2.3.0/gems/json-1.8.6/ext/json/ext/generator/usr/bin/ruby2.3 -r ./siteconf20170704-11395-12tpg5u.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/2.3.0/gems/json-1.8.6 for inspection.
  Results logged to /var/lib/gems/2.3.0/extensions/x86_64-linux/2.3.0/json-1.8.6/gem_make.out
  
  An error occurred while installing json (1.8.6), and Bundler cannot continue.
  Make sure that `gem install json -v '1.8.6'` succeeds before bundling
  </code></pre>
  
  <p>Kindly send me some suggestions,Thanks in Advance.</p>