docs: def clear(self, username, project):
          """Clear the cache for given project."""
          method = 'DELETE'
          url = ('/project/{username}/{project}/build-cache?'
                 'circle-token={token}'.format(username=username,
                                               project=project,
                                               token=self.client.api_token))
          json_data = self.client.request(method, url)
          return json_data