Double send of signal

[Tatsuya Matoba]

There is double send of signal as below at develop branch.

https://github.com/azavea/django-amazon-ses/blob/develop/django_amazon_ses.py#L122-L125

            message_id = result["MessageId"]
            post_send.send(self.__class__, message=email_message, message_id=message_id)
            message_id = result["MessageId"]
            post_send.send(self.__class__, message=email_message, message_id=message_id)

There is not double send in PR. #45

But it included at 694207c .

I think it mistake of cherypick.

[Hector Castro]

Hey @mtb-beta, thanks for pointing this out. The fix was included in the 3.0.1 release: https://github.com/azavea/django-amazon-ses/releases/tag/3.0.1.