Minor grammar edit to DataSourceUpdateMode (#4460)

Minor grammar edit

Author: shdvr

xml/System.Windows.Forms/DataSourceUpdateMode.xml

@@ -25,7 +25,7 @@
  When the update mode is Never, you can force the data source to be updated by using the <xref:System.Windows.Forms.Binding.WriteValue%2A> method.  
   
 > [!NOTE]
->  Even when the update mode is set to Never, the data source will be updated when the binding is first created, so at that least one update will always occur.  
+>  Even when the update mode is set to Never, the data source will be updated when the binding is first created, so at least one update will always occur.  
   
  ]]></format>
     </remarks>