Set python version in the travis matrix
Set python version in the travis matrix

dietsche/letsencrypt,thanatos/lets-encrypt-preview,wteiken/letsencrypt,twstrike/le_for_patching,stweil/letsencrypt,thanatos/lets-encrypt-preview,twstrike/le_for_patching,DavidGarciaCat/letsencrypt,wteiken/letsencrypt,mitnk/letsencrypt,dietsche/letsencrypt,TheBoegl/letsencrypt,lmcro/letsencrypt,jsha/letsencrypt,brentdax/letsencrypt,mitnk/letsencrypt,lmcro/letsencrypt,DavidGarciaCat/letsencrypt,jtl999/certbot,TheBoegl/letsencrypt,letsencrypt/letsencrypt,letsencrypt/letsencrypt,stweil/letsencrypt,jsha/letsencrypt,bsmr-misc-forks/letsencrypt,brentdax/letsencrypt,jtl999/certbot,bsmr-misc-forks/letsencrypt