Fields section of union documentation is formatted weirdly in rustdoc

[burtonageo]

When looking at the generated documentation for a union (e.g. https://docs.rs/MacTypes-sys/2.0.2/MacTypes_sys/union.NumVersionVariant.html), each field in the 'Fields' section is laid out on the same line:

parts: NumVersion whole: UInt32 

It would be nicer if they were laid out vertically as they are in structs (e.g. https://docs.rs/MacTypes-sys/2.0.2/MacTypes_sys/struct.FixedRect.html)