Fix typo in Task.xml (dotnet#5312)

* Fix typo in Task.xml

The sentence:

> ...the app may terminate before any the task actually begins execution...

Should read:

> ...the app may terminate before the task actually begins execution...

* Apply suggestions from code review

Co-authored-by: Adam Sitnik <[email protected]>

Author: ericmutta

xml/System.Threading.Tasks/Task.xml

@@ -119,7 +119,7 @@
   
 <a name="WaitingForOne"></a>   
 ## Waiting for one or more tasks to complete  
- Because tasks typically run asynchronously on a thread pool thread, the thread that creates and starts the task continues execution as soon as the task has been instantiated. In some cases, when the calling thread is the main application thread, the app may terminate before any the task actually begins execution. In others,   your application's logic may require that the calling thread continue execution only when one or more tasks has completed execution. You can synchronize the execution of the calling thread and the asynchronous tasks it launches by calling a `Wait` method to wait for one or more tasks to complete.  
+ Because tasks typically run asynchronously on a thread pool thread, the thread that creates and starts the task continues execution as soon as the task has been instantiated. In some cases, when the calling thread is the main application thread, the app may terminate before the task actually begins execution. In others, your application's logic may require that the calling thread continue execution only when one or more tasks have completed execution. You can synchronize the execution of the calling thread and the asynchronous tasks it launches by calling a `Wait` method to wait for one or more tasks to complete.  
   
  To wait for a single task to complete, you can call its <xref:System.Threading.Tasks.Task.Wait%2A?displayProperty=nameWithType> method. A call to the  <xref:System.Threading.Tasks.Task.Wait%2A> method blocks the calling thread until the single class instance has completed execution.