Fix example cleanup

Author: thomasp85

R/agg_dev.R

@@ -342,7 +342,8 @@ agg_capture <- function(width = 480, height = 480, units = 'px', pointsize = 12,
 #' dev.off()
 #'
 #' # Replay these on another device
-#' agg_png()
+#' file <- tempfile(fileext = '.png')
+#' agg_png(file)
 #' replayPlot(rec)
 #' dev.off()
 #'