mke2fs.conf: Use the feature name "extent" instead of "extents"

The feature name "extent" is documented in mke2fs.conf, although both
"extent" and "extents" are accepted by e2fsprogs.

Addreses-Debian-Bug: #540111

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/misc/mke2fs.conf b/misc/mke2fs.conf
index 3795b1e..52fe58e 100644
--- a/misc/mke2fs.conf
+++ b/misc/mke2fs.conf
@@ -9,11 +9,11 @@
 		features = has_journal
 	}
 	ext4 = {
-		features = has_journal,extents,huge_file,flex_bg,uninit_bg,dir_nlink,extra_isize
+		features = has_journal,extent,huge_file,flex_bg,uninit_bg,dir_nlink,extra_isize
 		inode_size = 256
 	}
 	ext4dev = {
-		features = has_journal,extents,huge_file,flex_bg,uninit_bg,dir_nlink,extra_isize
+		features = has_journal,extent,huge_file,flex_bg,uninit_bg,dir_nlink,extra_isize
 		inode_size = 256
 		options = test_fs=1
 	}