Update posts/2019-11-07-Rust-1.39.0.md

Author: Centril

posts/2019-11-07-Rust-1.39.0.md

@@ -26,7 +26,7 @@ The highlights of Rust 1.39.0 include `async`/`.await`, shared references to by-
 
 [rel-1360]: https://blog.rust-lang.org/2019/07/04/Rust-1.36.0.html#the-future-is-here
 [`Future`]: https://doc.rust-lang.org/nightly/std/future/trait.Future.html
-[niko-post-async]: TODO
+[niko-post-async]: https://blog.rust-lang.org/2019/11/07/Async-await-stable.html
 
 Previously in Rust 1.36.0, [we announced][rel-1360] that the [`Future`] trait is here. Back then, we noted that: