updating to toml 0.8

[plugwash]

Hi.

In debian we are looking to upgrade the rust-toml package from 0.7 to 0.8. While we do have a mechanism for packaging multiple versions of a crate it is something we try to avoid where possible. I was able to run the tests successfully with the dependency bumped, but there is one thing that gives me pause in the toml changelog.

Serialization and deserialization of tuple variants has changed from being an array to being a table with the key being the variant name and the value being the array

I would appreciate feedback on whether you consider this likely to be an issue for cargo-outdated.