xfs: fix kernel version in docs

Linux v3.20 was released as v4.0.

Signed-off-by: Fanael Linithien <fanael4@gmail.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

Documentation/filesystems/xfs.txt

@@ -236,10 +236,10 @@ Removed Mount Options
 
   Name				Removed
   ----				-------
-  delaylog/nodelaylog		v3.20
-  ihashsize			v3.20
-  irixsgid			v3.20
-  osyncisdsync/osyncisosync	v3.20
+  delaylog/nodelaylog		v4.0
+  ihashsize			v4.0
+  irixsgid			v4.0
+  osyncisdsync/osyncisosync	v4.0
 
 
 sysctls
@@ -346,5 +346,5 @@ Removed Sysctls
 
   Name				Removed
   ----				-------
-  fs.xfs.xfsbufd_centisec	v3.20
-  fs.xfs.age_buffer_centisecs	v3.20
+  fs.xfs.xfsbufd_centisec	v4.0
+  fs.xfs.age_buffer_centisecs	v4.0