docs/84408: dump(8) manpage doesn't require an option and has wrong default

[Gary W. Swearingen]

I was wrong about the "wrong default"; I forgot I had TAPE defined
when I tested.

The patch should have only been:

--- dump..orig.8	Sun Jul 31 11:11:22 2005
+++ dump.8	Sun Jul 31 11:18:27 2005
@@ -38,7 +38,7 @@
 .Nd file system backup
 .Sh SYNOPSIS
 .Nm
-.Op Fl 0123456789acLnSu
+.Fl 0123456789acLnSu
 .Op Fl B Ar records
 .Op Fl b Ar blocksize
 .Op Fl C Ar cachesize