Fixed outdated note in the tutorial

Author: aochagavia

src/doc/tutorial.md

@@ -2965,7 +2965,7 @@ use farm::*;
 ~~~
 
 > *Note:* This feature of the compiler is currently gated behind the
-> `#[feature(globs)]` directive. More about these directives can be found in
+> `#![feature(globs)]` directive. More about these directives can be found in
 > the manual.
 
 However, that's not all. You can also rename an item while you're bringing it into scope: