title: How to change the line type of ellipses in ggbiplot?
body: <p>Is it possible to change the type of lines of the normal probability ellipsoids in ggbiplot, e.g. have them dashed and dotted lines instead of or additional to the different colors? 
  I couldn't find anything in the documentation of ggbiplot except this to be used as MWE:</p>
  
  <pre><code>library(ggbiplot)
  data(wine)
  wine.pca &lt;- prcomp(wine, scale. = TRUE)
  print(ggbiplot(wine.pca, obs.scale = 1, var.scale = 1, groups = wine.class, ellipse = TRUE, circle = TRUE))
  </code></pre>