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`.
self._send_cors_headers()
                    self.end_headers()
                    return
            
            if response is None:
                forward_headers['Connection'] = forward_headers.get('Connection') or 'close'
                data_to_send = self.data_bytes
                request_url = proxy_url
                if modified_request:
                    if modified_request.url:
                        request_url = '%s%s' % (forward_url, modified_request.url)
                    data_to_send = modified_request.data
                response = self.method(request_url, data=data_to_send,
                    headers=forward_headers, stream=True)
                
                if not response._content_consumed and response.raw:
                    response._content = response.raw.read()
            
            if self.proxy.update_listener:
                kwargs = {
                    'method': method,
                    'path': path,
                    'data': data,
                    'headers': forward_headers,
                    'response': response
                }
                if 'request_handler' in inspect.getargspec(self.proxy.update_listener.return_response)[0]:
                    
                    
                    kwargs['request_handler'] = self