clippy_dev: port to edition 2018

clippy_dev/src/lib.rs

@@ -1,12 +1,9 @@
 #![feature(tool_lints)]
 #![allow(clippy::default_hash_types)]
-extern crate regex;
-#[macro_use]
-extern crate lazy_static;
-extern crate itertools;
 
-use regex::Regex;
 use itertools::Itertools;
+use lazy_static::lazy_static;
+use regex::Regex;
 use std::collections::HashMap;
 use std::ffi::OsStr;
 use std::fs;