Merge pull request #1729 from kberov/unused_label

Added attribute unused_labels - fixed warning.

Author: marioidival

src/flow_control/loop/nested.md

@@ -5,7 +5,7 @@ loops. In these cases, the loops must be annotated with some `'label`, and the
 label must be passed to the `break`/`continue` statement.
 
 ```rust,editable
-#![allow(unreachable_code)]
+#![allow(unreachable_code, unused_labels)]
 
 fn main() {
     'outer: loop {
@@ -26,4 +26,4 @@ fn main() {
 
     println!("Exited the outer loop");
 }
-```
+```