lint yaml files

.yamllint

dovecot/defaults/main.yml

dovecot/tasks/main.yml

postfix/defaults/main.yml

postfix/handlers/main.yml

postfix/tasks/main.yml

prosody/defaults/main.yml

prosody/tasks/main.yml

prosody/tasks/postgres.yml

spamassassin/defaults/main.yml

spamassassin/tasks/main.yml