Rollup merge of rust-lang#143340 - nabijaczleweli:awhile, r=mati865

awhile -> a while where appropriate

Author: matthiaskrgr

std/src/sync/mpmc/mod.rs

@@ -187,7 +187,7 @@ use crate::time::{Duration, Instant};
 ///     sender.send(expensive_computation()).unwrap();
 /// });
 ///
-/// // Do some useful work for awhile
+/// // Do some useful work for a while
 ///
 /// // Let's see what that answer was
 /// println!("{:?}", receiver.recv().unwrap());

std/src/sync/mpsc.rs

@@ -509,7 +509,7 @@ pub enum TrySendError<T> {
 ///     sender.send(expensive_computation()).unwrap();
 /// });
 ///
-/// // Do some useful work for awhile
+/// // Do some useful work for a while
 ///
 /// // Let's see what that answer was
 /// println!("{:?}", receiver.recv().unwrap());