Update Dependencies

Use flip/whoops 1.0.10 - no breaking changes there as far as i can see, just minor things, and an xml response handler.

Use aws/aws-sdk-php 2.5.* - a few changes there, you might want to check out https://github.com/aws/aws-sdk-php/blob/master/UPGRADING.md to make sure i haven't missed anything, but i don't think we need any code changes.