auto merge of rust-lang#15909 : colemickens/rust/patch-3, r=alexcrichton

Tested this on the playground, the range specifies range(0u, 3), so it should be okay to remove this cast.

Author: bors

src/doc/intro.md

@@ -276,7 +276,7 @@ fn main() {
 
         spawn(proc() {
             let numbers = rx.recv();
-            println!("{:d}", numbers[num as uint]);
+            println!("{:d}", numbers[num]);
         })
     }
 }