Fix a typo in the README.
Fix a typo in the README.

kangaderoo/vanitygen,sobakasu/vanitygen,kangaderoo/vanitygen,bespike/vanitygen,enlighter/vanitygen,inuitwallet/vanitygen,sobakasu/vanitygen,dooglus/vanitygen,kangaderoo/vanitygen,WyseNynja/vanitygen,dooglus/vanitygen,samr7/vanitygen,sobakasu/vanitygen,Stoner19/NEOS-vanitygen,Cremator/vanitygen,fantomgs/vanitygen,WyseNynja/vanitygen,bither/vanitygen,colindean/vanitygen,shinohai/vanitygen,clovermebitcoin/test,Instigo/vanitygen,Cremator/vanitygen,Gamecredits-Universe/vanitygen-gamecredits,isghe/vanitygen,enlighter/vanitygen,clovermebitcoin/test