Bump socket2 from 0.3.12 to 0.3.19 in /2020/GoogleCTF-2020/tracing

Bumps [socket2](https://github.com/rust-lang/socket2) from 0.3.12 to 0.3.19.
- [Release notes](https://github.com/rust-lang/socket2/releases)
- [Changelog](https://github.com/rust-lang/socket2/blob/master/CHANGELOG.md)
- [Commits](rust-lang/socket2@0.3.12...v0.3.19)

---
updated-dependencies:
- dependency-name: socket2
  dependency-type: indirect
...

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