Remove more extra spaces

exercise/threads_channels/src/main.rs

@@ -80,7 +80,7 @@ fn main() {
 
         // Using a Receiver channel as an iterator is a convenient way to get values until the channel
         // gets closed. A Receiver channel is automatically closed once all Sender channels have been
-        // closed.  Both our threads automatically close their Sender channels when they exit and the
+        // closed. Both our threads automatically close their Sender channels when they exit and the
         // destructors for the channels get automatically called.
         for msg in rx {
             println!("Main thread: Received {}", msg);
@@ -90,10 +90,10 @@ fn main() {
         // - Use the thread handles to join both threads without getting any compiler warnings.
     */
 
-    // Challenge: Make two child threads and give them each a receiving end to a channel.  From the
+    // Challenge: Make two child threads and give them each a receiving end to a channel. From the
     // main thread loop through several values and print each out and then send it to the channel.
     // On the child threads print out the values you receive. Close the sending side in the main
-    // thread by calling `drop(tx)` (assuming you named your sender channel variable `tx`).  Join
+    // thread by calling `drop(tx)` (assuming you named your sender channel variable `tx`). Join
     // the child threads.
     println!("Main thread: Exiting.")
 }