Apply typo fix from NetBSD, we have already applied all NetBSD changes so

update the NetBSD tag while I'm there.

MFC after:	2 weeks

sbin/fsck_msdosfs/boot.c

@@ -28,7 +28,7 @@
 
 #include <sys/cdefs.h>
 #ifndef lint
-__RCSID("$NetBSD: boot.c,v 1.11 2006/06/05 16:51:18 christos Exp ");
+__RCSID("$NetBSD: boot.c,v 1.21 2018/02/08 09:05:17 dholland Exp $");
 static const char rcsid[] =
   "$FreeBSD$";
 #endif /* not lint */
@@ -356,7 +356,7 @@ writefsinfo(int dosfs, struct bootblock *boot)
 	 * support for FAT32) doesn't maintain the FSINFO block
 	 * correctly, it has to be fixed pretty often.
 	 *
-	 * Therefor, we handle the FSINFO block only informally,
+	 * Therefore, we handle the FSINFO block only informally,
 	 * fixing it if necessary, but otherwise ignoring the
 	 * fact that it was incorrect.
 	 */