title: The option `lty` in `plot()` not working
body: <p>I am trying to generate a plot as interrupted line. But to my surprise the option <code>lty=2</code> in the function <code>plot()</code> doesnt work:</p>
  
  <pre><code>plot(1:10,lty=2) 
  </code></pre>
  
  <p>Can someone help me?</p>