message: Update documentation code.
diff: @@ -359,6 +359,7 @@ impl Bencher {
  /// # Example
  /// ```rust
  /// #[macro_use] extern crate criterion;
  + /// use criterion::*;
  /// use criterion::black_box;
  /// use std::time::Instant;
  ///
  @@ -368,7 +369,7 @@ impl Bencher {
  ///
  /// fn bench(c: &mut Criterion) {
  /// c.bench_function("iter", move |b| {
  - /// b.iter_custom(|| {
  + /// b.iter_custom(|iters| {
  /// let start = Instant::now();
  /// for _i in 0..iters {
  /// black_box(foo());
  