title: Center Plot title in ggplot2 using theme_bw
body: <p>Titles are left-aligned by default starting with ggplot 2.2.0. To make them centered again has already been explained in this post:</p>
  
  <p><a href="https://stackoverflow.com/questions/40675778/center-plot-title-in-ggplot2">Center Plot title in ggplot2</a></p>
  
  <p>This works perfectly in my case as well, however not if I use theme_bw.</p>
  
  <pre><code>dat &lt;- data.frame(
    time = factor(c("Lunch","Dinner"), levels=c("Lunch","Dinner")),
    total_bill = c(14.89, 17.23)
  )
  
  ggplot(data=dat, aes(x=time, y=total_bill, fill=time)) + 
    geom_bar(colour="black", fill="#DD8888", width=.8, stat="identity") + 
    guides(fill=FALSE) +
    xlab("Time of day") + ylab("Total bill") +
    ggtitle("Average bill for 2 people")+
    theme(plot.title = element_text(hjust = 0.5))+
    theme_bw()
  </code></pre>
  
  <p>I tried passing the theme arguments to <code>theme_bw()</code></p>
  
  <pre><code>theme_bw(plot.title = element_text(hjust = 0.5))
  </code></pre>
  
  <p>but that did`t work either.</p>
  
  <p>Any ideas? Help is much appreciated</p>