deps: update acorn to v8.0.4

This adds support for nullish coalescing, optional chaining and
numeric separators.
The acorn-numeric-separator plugin can be removed.

PR-URL: https://github.com/nodejs/node/pull/35791


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Shelley Vohr <codebytere@gmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>