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.quiet = quiet
        if self.httpd:
            self.httpd.server_close()
            self.server_stopped = True
    @classmethod
    def create_ssl_cert(cls, serial_number=None):
        return generate_ssl_cert(SERVER_CERT_PEM_FILE, serial_number=serial_number)
    @classmethod
    def get_flask_ssl_context(cls, serial_number=None):
        if USE_SSL:
            combined_file, cert_file_name, key_file_name = cls.create_ssl_cert(serial_number=serial_number)
            return (cert_file_name, key_file_name)
        return None
def serve_flask_app(app, port, quiet=True, host=None, cors=True):
    if cors:
        CORS(app)
    if quiet:
        logging.getLogger('werkzeug').setLevel(logging.ERROR)
    if not host:
        host = '0.0.0.0'
    ssl_context = GenericProxy.get_flask_ssl_context(serial_number=port)
    app.config['ENV'] = 'development'
    def noecho(*args, **kwargs):
        pass
    click.echo = noecho
    app.run(port=int(port), threaded=True, host=host, ssl_context=ssl_context)
    return app