Update itertools requirement from 0.12.0 to 0.13.0 (#13)

Author: dependabot[bot]

Cargo.toml

@@ -27,7 +27,7 @@ bytes = { version = "1.2.1", optional = true }
 serde = { version = "1.0", features = ["derive"] }
 assert_matches = "1.5.0"
 generator = "0.7"
-itertools = "0.12.0"
+itertools = "0.13.0"
 
 [package.metadata.docs.rs]
 all-features = true