Fix a warning.

Author: SimonSapin

build.rs

@@ -2,7 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-#[macro_use] extern crate quote;
+extern crate quote;
 extern crate syn;
 
 use std::env;