Bump serde_json from 1.0.67 to 1.0.68

Bumps [serde_json](https://github.com/serde-rs/json) from 1.0.67 to 1.0.68.
- [Release notes](https://github.com/serde-rs/json/releases)
- [Commits](https://github.com/serde-rs/json/compare/v1.0.67...v1.0.68)

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

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

Cargo.toml

@@ -26,7 +26,7 @@ blakeout = "0.3.0"
 num_cpus = "1.13.0"
 byteorder = "1.4.3"
 serde = { version = "1.0.130", features = ["derive"] }
-serde_json = "1.0.67"
+serde_json = "1.0.68"
 bincode = "1.3.3"
 serde_cbor = "0.11.2"
 base64 = "0.13.0"