Update ThreadPool.xml (#3922)

I was reading through the documentation and found what I believe to be a grammatical error on line 72.
The original text below

"The thread pool provides new worker threads or I/O completion threads on demand until it reaches the minimum for each category. When a minimum is reached, the thread pool can create additional threads in that category or wait until some tasks complete."

Author: Victor

xml/System.Threading/ThreadPool.xml

@@ -73,7 +73,7 @@
 > [!NOTE]
 >  Unmanaged code that hosts the .NET Framework can change the size of the thread pool by using the `CorSetMaxThreads` function, defined in the mscoree.h file.  
   
- The thread pool provides new worker threads or I/O completion threads on demand until it reaches the minimum for each category. When a minimum is reached, the thread pool can create additional threads in that category or wait until some tasks complete. Beginning with the [!INCLUDE[net_v40_short](~/includes/net-v40-short-md.md)], the thread pool creates and destroys worker threads in order to optimize throughput, which is defined as the number of tasks that complete per unit of time. Too few threads might not make optimal use of available resources, whereas too many threads could increase resource contention.  
+ The thread pool provides new worker threads or I/O completion threads on demand until it reaches the maximum for each category. When a maximum is reached, the thread pool can create additional threads in that category or wait until some tasks complete. Beginning with the [!INCLUDE[net_v40_short](~/includes/net-v40-short-md.md)], the thread pool creates and destroys worker threads in order to optimize throughput, which is defined as the number of tasks that complete per unit of time. Too few threads might not make optimal use of available resources, whereas too many threads could increase resource contention.  
   
 > [!NOTE]
 >  When demand is low, the actual number of thread pool threads can fall below the minimum values.