repl: display error message when loading directory

When loading directory instead of file, no error message
is displayed. It's good to display error message for
this scenario.

PR-URL: https://github.com/nodejs/node/pull/4170


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Minwoo Jung <jmwsoft@gmail.com>