silence AsciiExt deprecation warn

src/header/common/mod.rs

@@ -73,7 +73,7 @@ macro_rules! test_header {
     ($id:ident, $raw:expr) => {
         #[test]
         fn $id() {
-            #[allow(unused)]
+            #[allow(unused, deprecated)]
             use std::ascii::AsciiExt;
             use test;
             let raw = $raw;

src/header/shared/charset.rs

@@ -1,6 +1,7 @@
-#![allow(unused)]
+#![allow(unused, deprecated)]
 use std::fmt::{self, Display};
 use std::str::FromStr;
+use std::ascii::AsciiExt;
 
 use self::Charset::*;
 

src/header/shared/quality_item.rs

@@ -1,4 +1,4 @@
-#![allow(unused)]
+#![allow(unused, deprecated)]
 use std::ascii::AsciiExt;
 use std::cmp;
 use std::default::Default;