Update WaitHandle.cs (#8970)

Author: SamiSuleiman

snippets/csharp/System.Threading/WaitHandle/Overview/WaitHandle.cs

@@ -30,7 +30,7 @@ static void Main()
             (DateTime.Now - dt).TotalMilliseconds);
 
         // Queue up two tasks on two different threads;
-        // wait until any tasks are completed.
+        // wait until any task is completed.
         dt = DateTime.Now;
         Console.WriteLine();
         Console.WriteLine("The main thread is waiting for either task to complete.");
@@ -64,4 +64,4 @@ static void DoTask(Object state)
 //  Performing a task for 2000 milliseconds.
 //  Performing a task for 2000 milliseconds.
 //  Task 1 finished first (time waited=2000.6528).
-//</snippet1>
+//</snippet1>