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.function_invoke_times = {}
    def execute(self, func_arn, func_details, event, context=None, version=None, asynchronous=False):
        def do_execute(*args):
            
            invocation_time = int(time.time() * 1000)
            
            try:
                result, log_output = self._execute(func_arn, func_details, event, context, version)
            finally:
                self.function_invoke_times[func_arn] = invocation_time
            
            self._store_logs(func_details, log_output, invocation_time)
            
            return result, log_output
        
        if asynchronous:
            LOG.debug('Lambda executed in Event (asynchronous) mode, no response from this '
                      'function will be returned to caller')
            FuncThread(do_execute).start()
            return None, 'Lambda executed asynchronously.'
        return do_execute()
    def _execute(self, func_arn, func_details, event, context=None, version=None):
        """ This method must be overwritten by subclasses. """
        raise Exception('Not implemented.')
    def startup(self):