doc: "0" listed as possible value for "positive integer" values

Documentation mentions at

- https://rust-lang.github.io/rustfmt/?version=v1.8.0&search=#inline_attribute_width
- https://rust-lang.github.io/rustfmt/?version=v1.8.0&search=#enum_discrim_align_threshold

```
Default value: 0
Possible values: any positive integer
```

This is misleading/contradicting because 0 is not a positive integer.