test: fix broken assertion

This commit fixes a broken assertion in test-cli-eval.js.

PR-URL: https://github.com/nodejs/node/pull/10840


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Italo A. Casas <me@italoacasas.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>