stream: correct iterators in doc examples
Correct the iterators used in examples to produce
the described output.
//! #
//! # use async_std::prelude::*;
//! # use async_std::stream;
-//! let mut values = stream::repeat(1u8).take(5);
+//! let mut values = stream::from_iter(1u8..6);
//!
//! while let Some(x) = values.next().await {
//! println!("{}", x);
//!
//! Unlike `std::iter::IntoIterator`, `IntoStream` does not have compiler
//! support yet. This means that automatic conversions like with `for` loops
-//! doesn't occur yet, and `into_stream` will always have to be called manually.
+//! doesn't occur yet, and `into_stream` or `from_iter` as above will always
+//! have to be called manually.
//!
//! [`IntoStream`]: trait.IntoStream.html
//! [`into_stream`]: trait.IntoStream.html#tymethod.into_stream
//! #
//! # use async_std::prelude::*;
//! # use async_std::stream;
-//! let numbers = stream::repeat(1u8);
+//! let numbers = stream::from_iter(0u8..);
//! let mut five_numbers = numbers.take(5);
//!
//! while let Some(number) = five_numbers.next().await {
