Update changelog to reflect 0.18.0 (#5081)
Update changelog to reflect 0.18.0 (#5081)


jsha/letsencrypt,lmcro/letsencrypt,stweil/letsencrypt,lmcro/letsencrypt,letsencrypt/letsencrypt,jsha/letsencrypt,letsencrypt/letsencrypt,stweil/letsencrypt