build(deps): bump serde from 1.0.136 to 1.0.137

Bumps [serde](https://github.com/serde-rs/serde) from 1.0.136 to 1.0.137.
- [Release notes](https://github.com/serde-rs/serde/releases)
- [Commits](serde-rs/serde@v1.0.136...v1.0.137)

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

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

zebra-chain/Cargo.toml

@@ -37,7 +37,7 @@ lazy_static = "1.4.0"
 rand_core = "0.6.3"
 ripemd = "0.1.1"
 
-serde = { version = "1.0.136", features = ["serde_derive", "rc"] }
+serde = { version = "1.0.137", features = ["serde_derive", "rc"] }
 serde_with = "1.13.0"
 serde-big-array = "0.4.1"
 # Matches version used by hdwallet