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

[ensc]

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.

[ytmimi]

Please open a PR for this if you have any suggestions for clarifying the docs.