benchmark: add final clean-up to module-loader.js

PR-URL: https://github.com/nodejs/node/pull/12102
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>

benchmark/module/module-loader.js

@@ -34,6 +34,8 @@ function main(conf) {
     measureFull(n);
   else
     measureDir(n);
+
+  rmrf(tmpDirectory);
 }
 
 function measureFull(n) {