Added missing plural to the work "block" (#4191)

"Dataflow block*s* capture the state of the options at their construction."

Author: maslisko

xml/System.Threading.Tasks.Dataflow/ExecutionDataflowBlockOptions.xml

@@ -46,7 +46,7 @@
 |BoundedCapacity|DataflowBlockOptions.Unbounded (-1)|  
 |MaxDegreeOfParallelism|1|  
   
- Dataflow block capture the state of the options at their construction. Subsequent changes to the provided <xref:System.Threading.Tasks.Dataflow.ExecutionDataflowBlockOptions> instance should not affect the behavior of a dataflow block.  
+ Dataflow blocks capture the state of the options at their construction. Subsequent changes to the provided <xref:System.Threading.Tasks.Dataflow.ExecutionDataflowBlockOptions> instance should not affect the behavior of a dataflow block.  
   
  ]]></format>
     </remarks>