allow mailer-ses to use other regions, still defaults to us-east-1

SES is available in multiple regions: http://docs.aws.amazon.com/ses/latest/DeveloperGuide/regions.html

aws-ses gem supports "server": https://github.com/drewblas/aws-ses#connecting-to-a-server-from-another-region

This patch allows us to use mailer-ses with other regions.