Update monero requirement from 0.17 to 0.18 (monero-rs#83)

Updates the requirements on [monero](https://github.com/monero-rs/monero-rs) to permit the latest version.
- [Release notes](https://github.com/monero-rs/monero-rs/releases)
- [Changelog](https://github.com/monero-rs/monero-rs/blob/main/CHANGELOG.md)
- [Commits](monero-rs/monero-rs@v0.17.0...v0.18.0)

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

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Cargo.toml

@@ -17,7 +17,7 @@ fixed-hash = "0.7"
 hex = "0.4"
 http = "0.2"
 jsonrpc-core = "18"
-monero = { version = "0.17", features = ["serde"] }
+monero = { version = "0.18", features = ["serde"] }
 reqwest = { version = "0.11", features = ["json"] }
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"