Fix Travis tests due to cffi error
Fix Travis tests due to cffi error

jsha/letsencrypt,jsha/letsencrypt,letsencrypt/letsencrypt,stweil/letsencrypt,jtl999/certbot,bsmr-misc-forks/letsencrypt,lmcro/letsencrypt,letsencrypt/letsencrypt,lmcro/letsencrypt,stweil/letsencrypt,jtl999/certbot,bsmr-misc-forks/letsencrypt