code: def add_version(self, project, version, egg):
          
          url = self._build_url(constants.ADD_VERSION_ENDPOINT)
          data = {
              'project': project,
              'version': version
          }
          files = {
              'egg': egg
          }
          json = self.client.post(url, data=data, files=files,
                                  timeout=self.timeout)
          return json['spiders']
docs: Adds a new project egg to the Scrapyd service. First class, maps to
          Scrapyd's add version endpoint.