Missing notifcationType in SimpleEmailService

[kaihendry]

https://github.com/aws/aws-lambda-go/blob/master/events/ses.go#L16

Put https://s.natalian.org/2018-09-13/ses.json into https://mholt.github.io/json-to-go/

[kaihendry]

Furthermore https://github.com/aws/aws-lambda-go/blob/master/events/ses.go#L58-L62 is missing details like topicArn, bucketName, objectKey et al

[LegNeato]

Please put up a PR with the changes plus an example event.

[bmoffatt]

resolved by #211