doc: fix vm.runInNewContext signature

The `options` parameter cannot be passed without `sandbox`.

PR-URL: https://github.com/nodejs/node/pull/21824


Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>