Remove box syntax from rustc_serialize

compiler/rustc_serialize/src/lib.rs

@@ -9,7 +9,6 @@ Core encoding and decoding interfaces.
     html_playground_url = "https://play.rust-lang.org/",
     test(attr(allow(unused_variables), deny(warnings)))
 )]
-#![feature(box_syntax)]
 #![feature(never_type)]
 #![feature(nll)]
 #![feature(associated_type_bounds)]

compiler/rustc_serialize/src/serialize.rs

@@ -679,6 +679,6 @@ impl<S: Encoder, T: ?Sized + Encodable<S>> Encodable<S> for Box<T> {
 }
 impl<D: Decoder, T: Decodable<D>> Decodable<D> for Box<T> {
     fn decode(d: &mut D) -> Result<Box<T>, D::Error> {
-        Ok(box Decodable::decode(d)?)
+        Ok(Box::new(Decodable::decode(d)?))
     }
 }