Switch to 2018 edition use syntax

src/main.rs

@@ -1,15 +1,7 @@
 #![deny(warnings)]
-extern crate biscuit;
-extern crate base64;
-extern crate hyper;
-extern crate ldap3;
-extern crate tokio;
-
-#[macro_use] extern crate log;
-
-#[macro_use(Serialize)]
-extern crate serde_derive;
 
+use log::info;
+use serde_derive::Serialize;
 use std::env;
 use std::fs;
 use std::path::Path;