How to use the yamljs.dump function in yamljs

new Promise((resolve, reject) => {
            const contributors = JSON.parse(content).contributors.map(c => {
              const avatar = url.parse(c['avatar_url'], true);
              avatar.search = undefined; // Override so that we can use `avatar.query`.
              if (avatar.hostname.endsWith('githubusercontent.com')) {
                // Use 32px avatars, instead of full-size.
                avatar.query['s'] = '32';
              }
              const avatar_url = url.format(avatar);
              return Object.assign({}, c, { avatar_url });
            });
            resolve(yaml.dump({ contributors }));
          })
      )

get: function(yaml) {
                yaml = yaml || false;
                if (validate()) {
                    return (yaml ? YAML.dump(spec,100,2): JSON.stringify(spec, null, 2));
                } else {
                    console.error('Errors found when validating generated Swagger');
                    return false;
                }
            }
        };