Update DeflateStream.xml (#3891)

The current implementation of `Flush` **does** flush the internal buffer.

Author: AroglDarthu

xml/System.IO.Compression/DeflateStream.xml

@@ -1035,7 +1035,7 @@ The end write call is invalid.</exception>
           <format type="text/markdown"><![CDATA[  
   
 ## Remarks  
- The current implementation of this method does not flush the internal buffer. The internal buffer is flushed when the object is disposed.  
+ Flushes the internal buffer if the compression mode is set to <xref:System.IO.Compression.CompressionMode.Compress>.
   
  ]]></format>
         </remarks>