Remove the clippy plugin

And update instructions to run clippy from cargo

Cargo.toml

@@ -25,7 +25,6 @@ maintenance = { status = "passively-maintained" }
 
 [features]
 default = ["serde"]
-dev = ["clippy"]
 
 [[bench]]
 name = "parse_bench"

README.md

@@ -7,7 +7,8 @@ This is a library to work with IPv4 and IPv6 CIDRs in rust
 
 Run Clippy by doing
 ```
-cargo test --features "dev"
+rustup component add clippy
+cargo clippy
 ```
 
 ### Installation

src/lib.rs

@@ -1,7 +1,5 @@
 //! The `ipnetwork` crate provides a set of APIs to work with IP CIDRs in
 //! Rust.
-#![cfg_attr(feature = "dev", feature(plugin))]
-#![cfg_attr(feature = "dev", plugin(clippy))]
 #![crate_type = "lib"]
 #![doc(html_root_url = "https://docs.rs/ipnetwork/0.16.0")]