$ARG_0 variable to `version` hook of `exec` plugin not as implied by documentation

[The documentation for the `exec` plugin](https://intuit.github.io/auto/docs/generated/exec#usage) gives the following example:

```json
{
"plugins": [
[
"exec",
{
"version": "npm version $ARG_0",
"publish": "npm publish && git push --tags",
"afterRelease": "yarn docs && push-dir --dir=docs --branch=gh-pages"
}
]
// other plugins
]
}
```

This example strongly implies that, when using the `version` hook via `exec`, the `$ARG_0` envvar will be a valid argument to `npm version`, i.e., either a version string or a semantic version component name like "minor" or "patch". However, I am finding that it is actually a string of the form `{"bump":"minor"}`. Is the documentation wrong, or is `auto` bugged?

I have not checked any other `exec` hooks to see whether something similar applies to them.

**Environment information:**

GitHub Actions `ubuntu-latest` environment, using the latest `auto` downloaded from