Fix typo (#3874)

Author: jkotas

xml/System.Threading/WaitHandle.xml

@@ -890,7 +890,7 @@ Calling `Dispose` allows the resources used by the <xref:System.Threading.WaitHa
 
  -or-  
 
- The current thread is <see cref="F:System.Threading.ApartmentState.STA" /> state, and <paramref name="waitHandles" /> contains more than one element.</exception>
+ The current thread is in <see cref="F:System.Threading.ApartmentState.STA" /> state, and <paramref name="waitHandles" /> contains more than one element.</exception>
         <exception cref="T:System.ApplicationException">
           <paramref name="waitHandles" /> is an array with no elements and the .NET Framework version is 1.0 or 1.1.</exception>
         <exception cref="T:System.Threading.AbandonedMutexException">The wait terminated because a thread exited without releasing a mutex. This exception is not thrown on Windows 98 or Windows Millennium Edition.</exception>