Cookie field addition causing API gateway to returns 502 gateway error.

[fudanchii]

As per https://docs.aws.amazon.com/apigateway/latest/developerguide/set-up-lambda-proxy-integrations.html#api-gateway-simple-proxy-for-lambda-output-format API Gateway for lambda proxy expecting really specific format for its response payload.

The addition of a new field cookies since v0.7.0 apparently is causing responses from lambda functions to be rejected due to the restriction.

I think we can make the field cookies to be omitted if it's empty, or make it configurable for ridge to have separate response struct with and without cookies field addition.

I'm willing to push a PR for the change as this is also will help us in the long run, but would like to know if there is any interest for the fix.

Thank you!