Rollup merge of #81445 - ehuss:update-cargo, r=ehuss

Rollup merge of #81445 - ehuss:update-cargo, r=ehuss

Update cargo

7 commits in 783bc43c660bf39c1e562c8c429b32078ad3099b..c3abcfe8a75901c7c701557a728941e8fb19399e
2021-01-20 19:02:26 +0000 to 2021-01-25 16:16:43 +0000
- Minor update to tracking issue template. (rust-lang/cargo#9097)
- Add some extra help to `cargo new` and invalid package names. (rust-lang/cargo#9098)
- Fix compilation with serde 1.0.122 (rust-lang/cargo#9102)
- Add suggestion for bad package id. (rust-lang/cargo#9095)
- Remove Registry::new. (rust-lang/cargo#9093)
- Fix: set default git config search path for tests (rust-lang/cargo#9035)
- Unstable updates (rust-lang/cargo#9092)