adapt barplot syntax

vignettes/hitlercomparison.Rmd

@@ -169,5 +169,5 @@ hitler_comparison
 ```
 Finally, we want to plot our results:
 ```{r, fig.width=7}
-bar_plot_fraktionen(hitler_comparison, percent, fill=fraktion, title="Coincidence of party vocabulary with nazi vocabulary", ylab="unique 'nazi' words per total (unique) fraction words [%]")
+bar_plot_fraktionen(hitler_comparison, y_variable = percent, title="Coincidence of party vocabulary with nazi vocabulary", ylab="unique 'nazi' words per total (unique) fraction words [%]")
 ```