Fix typo in the 1.31.1 blog post

r? @steveklabnik

Author: pietroalbini

posts/2018-12-20-Rust-1.31.1.md

@@ -35,7 +35,7 @@ usage:](https://github.com/rust-lang/rls/pull/1170)
 ```rust
 /// Some documentation
 #[derive(Debug)] // Multiple, single-line
-#[allow(missing_docs)] // atributes
+#[allow(missing_docs)] // attributes
 pub struct MyStruct { /* ... */ }
 ```
 
@@ -50,4 +50,4 @@ and now RLS goes to the correct location (for Rust 1.31, note the extra `src`):
 
 ```text
 ~/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/collections/hash/map.rs
-```
+```