Auto merge of #64361 - ehuss:update-cargo, r=alexcrichton

Update cargo

11 commits in fe0e5a48b75da2b405c8ce1ba2674e174ae11d5d..9655d70af8a6dddac238e3afa2fec75088c9226f
2019-09-04 00:51:27 +0000 to 2019-09-10 18:16:11 +0000
- Home docs: fix broken links, misspellings, style fixes, clarifications. (rust-lang/cargo#7348)
- add readme key to cargos manifest. (rust-lang/cargo#7347)
- Explicitly ignore some results (rust-lang/cargo#7340)
- Don't resolve std's optional dependencies (rust-lang/cargo#7337)
- Add `alloc` and `proc_macro` to libstd crates (rust-lang/cargo#7336)
- doc: capitalization change for consistency. (rust-lang/cargo#7334)
- Fix test for changes in plugin API. (rust-lang/cargo#7335)
- Fix some man pages where the files weren't rebuilt. (rust-lang/cargo#7332)
- guide: add section about the cargo home (rust-lang/cargo#7314)
- `map_dependencies` is doing a deep clone, so lets make it cheaper (rust-lang/cargo#7326)
- don't need to copy this string (rust-lang/cargo#7324)