Fix mapping location.

#246

visualize.Rmd

@@ -280,8 +280,8 @@ If you prefer to not facet in the rows or columns dimension, use a `.` instead o
 1.  Take the first faceted plot in this section:
 
     ```{r, eval = FALSE}
-    ggplot(data = mpg, mapping = aes(x = displ, y = hwy)) + 
-      geom_point() + 
+    ggplot(data = mpg) + 
+      geom_point(mapping = aes(x = displ, y = hwy)) + 
       facet_wrap(~ class, nrow = 2)
     ```