title: rack requires Ruby version >= 2.2.2
body: <p>I'm trying to use <code>Travis-CI</code> with a new <code>Ruby on Rails</code> project I just started a few days ago. I've tried updating <code>Travis-CI</code> to update <code>rubygems</code> in <code>before_install</code> but still no luck.  </p>
  
  <pre><code>Gem::InstallError: rack requires Ruby version &gt;= 2.2.2.
  
  Installing nio4r 1.2.1
  
  An error occurred while installing rack (2.0.1), and Bundler cannot continue.
  
  Make sure that `gem install rack -v '2.0.1'` succeeds before bundling.
  </code></pre>