message: doc: fix return value of `match_indices` in pattern example
  PR
diff: @@ -129,7 +129,7 @@ impl<'t> From<Match<'t>> for Range<usize> {
  /// assert!(haystack.contains(&re));
  /// assert_eq!(haystack.find(&re), Some(1));
  /// assert_eq!(haystack.match_indices(&re).collect::<Vec<_>>(),
  -/// vec![(1, 4), (5, 8)]);
  +/// vec![(1, "111"), (5, "222")]);
  /// assert_eq!(haystack.split(&re).collect::<Vec<_>>(), vec!["a", "b", "c"]);
  /// ```
  #[derive(Clone)]
  