title: pROC ROC curves remove empty space
body: <p>I want to draw ROC curves with pRoC.
  However for some reason there is extra empty space on either side of the x-axis and I cannot remove it with xlim. Some example code:</p>
  
  <pre><code>library(pROC)
  n = c(4, 3, 5) 
  b = c(TRUE, FALSE, TRUE) 
  df = data.frame(n, b) 
  rocobj &lt;- plot.roc(df$b, df$n, percent = TRUE, main="ROC", col="#1c61b6", add=FALSE)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/fsiea.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fsiea.png" alt="enter image description here"></a></p>
  
  <p>I tried the pROC help file, but that doesn't really help me. Even more puzzling is to me that the Y-axis is OK looking...</p>
  
  <p>I really appreciate your help!</p>