fix missing backtick

Author: steveklabnik

_posts/2017-04-27-Rust-1.17.md

@@ -218,7 +218,7 @@ Now, you can write
 SocketAddr::from(([127, 0, 0, 1], 3000))
 // or even
 ([127, 0, 0, 1], 3000).into())
-``
+```
 
 This removes some unnecesary run-time parsing, and is roughly as readable, depending on
 your preferences.