Fix blog url

Closes #636

Author: alexcrichton

_config.yml

@@ -1,7 +1,7 @@
 name: The Rust Programming Language
 stable: "1.13.0"
 stable_date: "2016-11-10"
-stable_blog: "/2016/11/10/Rust-1.13.html"
+stable_blog: "https://blog.rust-lang.org/2016/11/10/Rust-1.13.html"
 stable_full_version: "rustc 1.13.0 (2c6933acc 2016-11-07)"
 beta: "1.14"
 beta_date: "2016-12-22"