title: Cant install ruby-switch for ruby on rails
body: <p>I am trying to install ruby on rails on Ubuntu via bright box. I've installed:</p>
  
  <pre><code>sudo apt-get install software-properties-common
  sudo apt-add-repository ppa:brightbox/ruby-ng
  sudo apt-get update
  
  sudo apt-get install ruby ruby-dev
  </code></pre>
  
  <p>But when I try to install this:</p>
  
  <pre><code>sudo apt-get install ruby-switch
  </code></pre>
  
  <p>I get this error:</p>
  
  <pre><code>Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  Package ruby-switch is not available, but is referred to by another package.
  This may mean that the package is missing, has been obsoleted, or
  is only available from another source
  
  E: Package 'ruby-switch' has no installation candidate
  </code></pre>
  
  <p>What is the problem, and how to solve it?</p>