Fix typo in README
Fix typo in README

Sup, me again. While I'm here... shouldn't the description for `--simple-output` be different from `--coveralls`?
domenicosolazzo/slather,robertofrontado/slather,xing/slather,nerdishbynature/slather,fikeminkel/slather,venmo/slather,fikeminkel/slather,mattdelves/slather,petester42/slather,domenicosolazzo/slather,mattdelves/slather,xing/slather,petester42/slather,nerdishbynature/slather,orta/slather,dmiedema/slather,nerdishbynature/slather,ben-ng/slather,RyanCopley/slather,tabuchid/slather,tarbrain/slather,neonichu/slather,domenicosolazzo/slather,RyanCopley/slather,fikeminkel/slather,viteinfinite/slather,orta/slather,petester42/slather,orta/slather,petester42/slather,xing/slather,RyanCopley/slather,mattdelves/slather,tabuchid/slather,dhardiman/slather,mattdelves/slather,fikeminkel/slather,tabuchid/slather,tabuchid/slather,nerdishbynature/slather,SlatherOrg/slather,AliSoftware/slather