title: YAML safe loading is not available
body: <p>When I want to install <code>compass</code> with <code>gem install compass</code>, I occurred with this error:</p>
  
  <pre><code>YAML safe loading is not available. 
  Please upgrade psych to a version that supports safe loading (&gt;= 2.0).
  </code></pre>
  
  <p><strong>what The cause of this error and how can I solve the problem?</strong></p>