build: Bump log from 0.4.17 to 0.4.20

Bumps [log](https://github.com/rust-lang/log) from 0.4.17 to 0.4.20.
- [Release notes](https://github.com/rust-lang/log/releases)
- [Changelog](https://github.com/rust-lang/log/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rust-lang/log/compare/0.4.17...0.4.20)

---
updated-dependencies:
- dependency-name: log
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

virtio-devices/Cargo.toml

@@ -15,7 +15,7 @@ byteorder = "1.4.3"
 epoll = "4.3.3"
 event_monitor = { path = "../event_monitor" }
 libc = "0.2.147"
-log = "0.4.17"
+log = "0.4.20"
 net_gen = { path = "../net_gen" }
 net_util = { path = "../net_util" }
 pci = { path = "../pci" }