The following example `serverless.yml` fails to deploy on localstack:

```yaml
service: "localtest"

provider:
  name: "aws"
  runtime: "nodejs10.x"

functions:
  hello:
    handler: "handler.hello"
    
resources:
  Resources:
    ApiGatewayRestApi:
      Type: "AWS::ApiGateway::RestApi"
      Properties:
        Name: "${self:provider.stage}-${self:service}"
    GatewayResponseDefault400:
      Type: "AWS::ApiGateway::GatewayResponse"
      Properties:
        RestApiId:
          Ref: "ApiGatewayRestApi"
        ResponseType: "DEFAULT_4XX"
        ResponseTemplates:
          application/json: '{"errors":[{"message":"Custom text."}]}'
    GatewayResponseUnauthorized:
      Type: "AWS::ApiGateway::GatewayResponse"
      Properties:
        RestApiId:
          Ref: "ApiGatewayRestApi"
        ResponseType: "UNAUTHORIZED"
        ResponseTemplates:
          application/json: '{"errors":[{"message":"Custom text!", "extra":"Some extra info"}]}'
    GatewayResponseDefault500:
      Type: "AWS::ApiGateway::GatewayResponse"
      Properties:
        RestApiId:
          Ref: "ApiGatewayRestApi"
        ResponseType: "DEFAULT_5XX"
        ResponseTemplates:
          application/json: '{"errors":[{"message":$context.error.messageString}]}'
    GatewayResponseIntegrationTimeout:
      Type: "AWS::ApiGateway::GatewayResponse"
      Properties:
        RestApiId:
          Ref: "ApiGatewayRestApi"
        ResponseType: "INTEGRATION_TIMEOUT"
        ResponseTemplates:
          application/json: '{"errors":[{"message":$context.error.messageString}]}'

plugins:
- "serverless-localstack"

custom:
  localstack:
    stages:
      - "local"
```

The error on the localstack end is `Exception: CloudFormation deployment for resource type ApiGateway::GatewayResponse not yet implemented`.
sm_name = resolve_refs_recursively(stack_name, sm_name, resources)
            sfn_client = aws_stack.connect_to_service('stepfunctions')
            state_machines = sfn_client.list_state_machines()['stateMachines']
            sm_arn = [m['stateMachineArn'] for m in state_machines if m['name'] == sm_name]
            if not sm_arn:
                return None
            result = sfn_client.describe_state_machine(stateMachineArn=sm_arn[0])
            return result
        elif resource_type == 'StepFunctions::Activity':
            act_name = resource_props.get('Name') or resource_id
            act_name = resolve_refs_recursively(stack_name, act_name, resources)
            sfn_client = aws_stack.connect_to_service('stepfunctions')
            activities = sfn_client.list_activities()['activities']
            result = [a['activityArn'] for a in activities if a['name'] == act_name]
            if not result:
                return None
            return result[0]
        if is_deployable_resource(resource):
            LOG.warning('Unexpected resource type %s when resolving references of resource %s: %s' %
                        (resource_type, resource_id, resource))
    except Exception as e:
        check_not_found_exception(e, resource_type, resource, resource_status)
    return None
def check_not_found_exception(e, resource_type, resource, resource_status):
    
    markers = ['NoSuchBucket', 'ResourceNotFound', '404']
    if not list(filter(lambda marker, e=e: marker in str(e), markers)):
        LOG.warning('Unexpected error retrieving details for resource %s: %s %s - %s %s' %
            (resource_type, e, traceback.format_exc(), resource, resource_status))
def extract_resource_attribute(resource_type, resource, attribute):