title: Curvilinear plots with sjplot
body: <p>I have a mixed model (using nlme) with time and time quadratic (time2). How can I let sjp.int (of sjplot) ask to plot it curvilinear?</p>
  
  <pre><code>   model = lme(MR ~ Age* time + sex*time + ed* time+ time* HMD+time2*HMD, random=~1|subject, na.action="na.omit",data=mydata);summary(model)
  </code></pre>
  
  <p>I called sjplot as: </p>
  
  <pre><code>  sjp.int(model, type="eff", swap.pred=T, mdrt.values="quart", show.ci=T)
  </code></pre>