Bump serde from 1.0.136 to 1.0.137 (#177)

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](https://github.com/serde-rs/serde/compare/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>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Cargo.toml

@@ -7,7 +7,7 @@ edition = "2018"
 [dependencies]
 sendgrid = { version = "0.17.4", default-features = false, features = ["rustls", "blocking"] }
 serde_derive = "1.0.112"
-serde = "1.0.136"
+serde = "1.0.137"
 reqwest = { version = "0.11", default-features = false, features = ["json", "rustls-tls"] }
 tokio = { version = "1.18", features = ["full"] }
 serde_json = "1.0.68"