benchmark: fixes csv parsing given no parameters

When a benchmark did not contain any parameters the csv configuration
filed would be "". In R this is by default parsed as NA, causing NA in
the printout too.

Fixes: https://github.com/nodejs/node/issues/9061
PR-URL: https://github.com/nodejs/node/pull/9064
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>

benchmark/compare.R

@@ -16,8 +16,12 @@ if (!is.null(args.options$help) ||
 
 plot.filename = args.options$plot;
 
-dat = read.csv(file('stdin'));
+dat = read.csv(
+  file('stdin'),
+  colClasses=c('character', 'character', 'character', 'numeric', 'numeric')
+);
 dat = data.frame(dat);
+
 dat$nameTwoLines = paste0(dat$filename, '\n', dat$configuration);
 dat$name = paste0(dat$filename, dat$configuration);