Add Clippy to the development-tools::cargo-plugins category

Author: mcarton

Cargo.toml

@@ -13,7 +13,7 @@ repository = "https://github.com/Manishearth/rust-clippy"
 readme = "README.md"
 license = "MPL-2.0"
 keywords = ["clippy", "lint", "plugin"]
-categories = ["development-tools"]
+categories = ["development-tools", "development-tools::cargo-plugins"]
 
 [badges]
 travis-ci = { repository = "Manishearth/rust-clippy" }