Update ipnetwork requirement from 0.20.0 to 0.21.0

Updates the requirements on [ipnetwork](https://github.com/achanda/ipnetwork) to permit the latest version.
- [Release notes](https://github.com/achanda/ipnetwork/releases)
- [Changelog](https://github.com/achanda/ipnetwork/blob/master/CHANGELOG.md)
- [Commits](achanda/ipnetwork@v0.20.0...v0.21.0)

---
updated-dependencies:
- dependency-name: ipnetwork
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Cargo.toml

@@ -23,7 +23,7 @@ name ="maxminddb"
 path = "src/maxminddb/lib.rs"
 
 [dependencies]
-ipnetwork = "0.20.0"
+ipnetwork = "0.21.0"
 log = "0.4"
 serde = { version = "1.0", features = ["derive"] }
 memchr = "2.4"