Fix typo in help text.
Fix typo in help text.

The typo has been introduced in the latest upstream merge.

pataquets/namecoin-core,namecoin/namecoin-core,domob1812/namecore,namecoin/namecoin-core,namecoin/namecore,namecoin/namecoin-core,pataquets/namecoin-core,pataquets/namecoin-core,namecoin/namecoin-core,namecoin/namecore,pataquets/namecoin-core,namecoin/namecoin-core,domob1812/namecore,pataquets/namecoin-core,domob1812/namecore,namecoin/namecore,domob1812/namecore,namecoin/namecoin-core,domob1812/namecore,domob1812/namecore,pataquets/namecoin-core,namecoin/namecore,namecoin/namecore,namecoin/namecore