Resolving `prettier` dependency

Due to issue with dependency resolving, you might end up a different version of `prettier` in project's `node_modules` and `node_modules/newspack-scripts/node_modules`.
To fix this and make `newspack-scripts` use to "root" version of `prettier`, remove the offending `prettier` version in a `postinstall` hook script:

```json
"postinstall": "rm -rf node_modules/newspack-scripts/node_modules/prettier"
```

---

This might be caused by version resolving being thrown off by aliasing `prettier` to [`wp-prettier`](https://www.npmjs.com/package/wp-prettier) as `npm:wp-prettier@2.2.1-beta-1`.

Technically it seems like the [`overrides` option](https://docs.npmjs.com/cli/v8/configuring-npm/package-json#overrides) should take care of that, but I did not have any luck with using it.