Update to Axum 0.4

[abonander]

According to the author of Axum, there should only be a couple small breaking changes: https://www.reddit.com/r/rust/comments/shetb1/show_rrust_a_rust_implementation_of_the_realworld/hv6ftnu/?context=3

[incon]

Updated all crates here #5 apart from the time crate.

[davidpdrsn]

I have made a fork of this repo https://github.com/davidpdrsn/realworld-axum-sqlx with up to date dependencies.