Fix JSHint error in benchmark/run

Fixes the following JSHint error:

  benchmark/run: line 106, col 10, Wrap the /regexp/ literal in parens to disambiguate the slash operator.

benchmark/run

@@ -103,7 +103,7 @@ function abort(message) {
 var args = process.argv.slice(2); // Trim "node" and the script path.
 
 function isOption(arg) {
-  return /^-/.test(arg);
+  return (/^-/).test(arg);
 }
 
 function nextArg() {