Update rocksdb requirement from 0.14 to 0.15

Updates the requirements on [rocksdb](https://github.com/rust-rocksdb/rust-rocksdb) to permit the latest version.
- [Release notes](https://github.com/rust-rocksdb/rust-rocksdb/releases)
- [Changelog](https://github.com/rust-rocksdb/rust-rocksdb/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rust-rocksdb/rust-rocksdb/compare/v0.14.0...v0.15.0)

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

lib/Cargo.toml

@@ -20,7 +20,7 @@ default = []
 sophia = ["sophia_api"]
 
 [dependencies]
-rocksdb = { version = "0.14", optional = true }
+rocksdb = { version = "0.15", optional = true }
 sled = { version = "0.34", optional = true }
 quick-xml = "0.18"
 rand = "0.7"