Boxes displayed around item names in docs in nightly

[brson]

See https://doc.rust-lang.org/nightly/std/io/trait.Read.html#method.chars. Every item has a one pixel black border that looks poor.

cc @bluss

[nagisa]

Similarly https://doc.rust-lang.org/nightly/std/io/trait.Read.html#method.read_exact has stabilisation version in a wrong place (caused by #38329). The linked commit may be the cause of this issue too.

[ollie27]

This was my bad. It was caused by #38329. Sorry about that. It should have been fixed by #38671.

[alexcrichton]

Closing now that #38671 landed, thanks @ollie27!