Improved the coverage of secretbox
Improved the coverage of secretbox

reaperhulk/pynacl,scholarly/pynacl,JackWink/pynacl,pyca/pynacl,pyca/pynacl,pyca/pynacl,pyca/pynacl,ucoin-io/cutecoin,pyca/pynacl,hoffmabc/pynacl,scholarly/pynacl,reaperhulk/pynacl,JackWink/pynacl,reaperhulk/pynacl,lmctv/pynacl,xueyumusic/pynacl,xueyumusic/pynacl,ucoin-io/cutecoin,ucoin-bot/cutecoin,lmctv/pynacl,scholarly/pynacl,reaperhulk/pynacl,lmctv/pynacl,ucoin-io/cutecoin,Insoleet/cutecoin,lmctv/pynacl,xueyumusic/pynacl,hoffmabc/pynacl,JackWink/pynacl,hoffmabc/pynacl,scholarly/pynacl,lmctv/pynacl,reaperhulk/pynacl,JackWink/pynacl,xueyumusic/pynacl