title: render html.erb template in sinatra
body: <p>How can render an <code>html.erb</code> template in sintara?</p>
  
  <p>For example, this works fine for a file named <code>payment.erb</code>:</p>
  
  <pre><code>&lt;%= render erb :payment %&gt;
  </code></pre>
  
  <p>The file I'm trying to use is named <code>payment.html.erb</code>, so what is the syntax for that <code>render</code> line?</p>