Simplify flat_map example

Author: mdinger

src/libcore/iter.rs

@@ -458,10 +458,9 @@ pub trait Iterator {
     /// # Examples
     ///
     /// ```
-    /// # #![feature(core)]
     /// let xs = [2, 3];
     /// let ys = [0, 1, 0, 1, 2];
-    /// let it = xs.iter().flat_map(|&x| (0..).take(x));
+    /// let it = xs.iter().flat_map(|&x| 0..x);
     /// // Check that `it` has the same elements as `ys`
     /// for (i, x) in it.enumerate() {
     ///     assert_eq!(x, ys[i]);