Downgrade libc and tracing-core

[zakiali]

Downgrading deps due to the following error when running cargo build:

error[E0599]: no method named `len` found for type `i8` in the current scope
   --> /Users/zaki/.cargo/registry/src/index.crates.io-6f17d22bba15001f/sysinfo-0.32.0/src/unix/apple/macos/process.rs:436:53
    |
436 |         Some(node.vip_path.len() * node.vip_path[0].len()),
    |                                                     ^^^
    |
help: there is a method `le` with a similar name, but with different arguments
   --> /rustc/f6e511eec7342f59a25f7c0534f1dbea00d01b14/library/core/src/cmp.rs:1196:5

libc and tracing-core had updated versions today that broke something. Not quite sure how these deps cause that error in sysinfo, but they are deps of it.