Add dev-dependencies keyword for serde_test

Author: dtolnay

serde_test/Cargo.toml

@@ -8,7 +8,7 @@ description = "Token De/Serializer for testing De/Serialize implementations"
 documentation = "https://docs.serde.rs/serde_test/"
 homepage = "https://serde.rs"
 include = ["build.rs", "src/**/*.rs", "crates-io.md", "README.md", "LICENSE-APACHE", "LICENSE-MIT"]
-keywords = ["serde", "serialization", "testing"]
+keywords = ["serde", "serialization", "testing", "dev-dependencies"]
 license = "MIT OR Apache-2.0"
 readme = "crates-io.md"
 repository = "https://github.com/serde-rs/serde"