Update C-NEWTYPE-HIDE now impl Trait is shipped

Author: dwijnand

src/future-proofing.md

@@ -108,10 +108,12 @@ less to the client. The client does not know _how_ the result iterator is
 constructed or represented, which means the representation can change in the
 future without breaking client code.
 
-In the future the same thing can be accomplished more concisely with the [`impl
-Trait`] feature but this is currently unstable.
+As of Rust 1.26 the same thing can be accomplished more concisely with the [`impl
+Trait`] feature.  See the ["`impl Trait` for returning complex types with ease"][impl-trait-2]
+section of the Edition Guide for more details.
 
 [`impl Trait`]: https://github.com/rust-lang/rfcs/blob/master/text/1522-conservative-impl-trait.md
+[impl-trait-2]: https://rust-lang-nursery.github.io/edition-guide/rust-2018/trait-system/impl-trait-for-returning-complex-types-with-ease.html
 
 ```rust
 #![feature(conservative_impl_trait)]