fix some cffi related warnings
fix some cffi related warnings

sholsapp/cryptography,Hasimir/cryptography,bwhmather/cryptography,Ayrx/cryptography,kimvais/cryptography,skeuomorf/cryptography,sholsapp/cryptography,bwhmather/cryptography,Ayrx/cryptography,skeuomorf/cryptography,kimvais/cryptography,Hasimir/cryptography,Hasimir/cryptography,kimvais/cryptography,kimvais/cryptography,sholsapp/cryptography,sholsapp/cryptography,Ayrx/cryptography,skeuomorf/cryptography,Ayrx/cryptography,bwhmather/cryptography,bwhmather/cryptography,skeuomorf/cryptography,Hasimir/cryptography