Support multiple different semver major dependencies on a single crate

[Nemo157]

In async-compression I support all of Tokio's ^0.2, ^0.3 and ^1.0 release branches as optional dependencies.

tokio-02 = { package = "tokio", version = "0.2.21", optional = true, default-features = false }
tokio-03 = { package = "tokio", version = "0.3.0", optional = true, default-features = false }
tokio = { version = "1.0.0", optional = true, default-features = false }

deps.rs chooses only the ^0.3 dependency to show (https://deps.rs/crate/async-compression/0.3.8):

Probably because it is the last of the 3 in the generated Cargo.toml. I'm not really sure how the UI could change to support situations like this better.