Use async_std::sync::Arc in examples (#501)

Author: Stjepan Glavina

src/stream/from_fn.rs

@@ -34,8 +34,7 @@ pin_project! {
 /// # async_std::task::block_on(async {
 /// #
 /// use async_std::prelude::*;
-/// use async_std::sync::Mutex;
-/// use std::sync::Arc;
+/// use async_std::sync::{Arc, Mutex};
 /// use async_std::stream;
 ///
 /// let count = Arc::new(Mutex::new(0u8));

src/sync/mod.rs

@@ -155,9 +155,7 @@
 //! ```
 //! # async_std::task::block_on(async {
 //! #
-//! use std::sync::Arc;
-//!
-//! use async_std::sync::Mutex;
+//! use async_std::sync::{Arc, Mutex};
 //! use async_std::task;
 //!
 //! let m1 = Arc::new(Mutex::new(0));

src/sync/mutex.rs

@@ -19,9 +19,7 @@ use crate::task::{Context, Poll};
 /// ```
 /// # async_std::task::block_on(async {
 /// #
-/// use std::sync::Arc;
-///
-/// use async_std::sync::Mutex;
+/// use async_std::sync::{Arc, Mutex};
 /// use async_std::task;
 ///
 /// let m = Arc::new(Mutex::new(0));
@@ -77,9 +75,7 @@ impl<T> Mutex<T> {
     /// ```
     /// # async_std::task::block_on(async {
     /// #
-    /// use std::sync::Arc;
-    ///
-    /// use async_std::sync::Mutex;
+    /// use async_std::sync::{Arc, Mutex};
     /// use async_std::task;
     ///
     /// let m1 = Arc::new(Mutex::new(10));
@@ -155,9 +151,7 @@ impl<T> Mutex<T> {
     /// ```
     /// # async_std::task::block_on(async {
     /// #
-    /// use std::sync::Arc;
-    ///
-    /// use async_std::sync::Mutex;
+    /// use async_std::sync::{Arc, Mutex};
     /// use async_std::task;
     ///
     /// let m1 = Arc::new(Mutex::new(10));