zfsprops.8: fix mispluralisation in "Default values is"

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: George Melikov <[email protected]>
Reviewed-by: Ryan Moeller <[email protected]>
Signed-off-by: Ahelenia Ziemiańska <[email protected]>
Closes #11509

Author: nabijaczleweli

man/man8/zfsprops.8

@@ -1766,7 +1766,7 @@ where
 and
 .Sy none
 are encoded as 1, 2 and 3 respectively.
-The default values is
+The default value is
 .Sy full .
 .It Sy vscan Ns = Ns Sy on Ns | Ns Sy off
 Controls whether regular files should be scanned for viruses when a file is