title: sprockets requires Ruby version >= 2.5.0 on rails 5
body: <p>I have rvm installed on my PC with the default ruby gemset being 2.4.1</p>
  
  <pre><code>rvm list
     ruby-2.4.0 [ x86_64 ]
  =* ruby-2.4.1 [ x86_64 ]
     ruby-2.6.3 [ x86_64 ]
  
  # =&gt; - current
  # =* - current &amp;&amp; default
  #  * - default
  </code></pre>
  
  <p>I want to install rails 5 however <code>sprockets</code> fails to install requiring 2.5 ruby. However rails 5 should work with any ruby above 2.2.2:</p>
  
  <pre><code>gem install rails -v 5.1.4
  Fetching: activesupport-5.1.4.gem (100%)
  Successfully installed activesupport-5.1.4
  Fetching: actionview-5.1.4.gem (100%)
  Successfully installed actionview-5.1.4
  Fetching: actionpack-5.1.4.gem (100%)
  Successfully installed actionpack-5.1.4
  ERROR:  Error installing rails:
      sprockets requires Ruby version &gt;= 2.5.0.
  </code></pre>
  
  <p>I don't care about the rails 5 version. The newer the better, but all versions do give me the errors</p>
  
  <p>Any idea why this might happen?</p>