Incorrect MethodResponses for APIGateway

[piersroberts]

MethodResponse parameters are expected to be Boolean, not String because as they are just a map to signify which parameters are REQUIRED not the expected string value.

https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-apitgateway-method-methodresponse.html#aws-properties-apitgateway-method-methodresponse-properties

This is causing Cloudformation validation errors when deploying stacks integrated with APIGateways

[rb62680]

This is a necessary fix. This is required to work with localstack for example.