code: function initDB () {
    return db.listDatabases()
      .then(response => {
        if (response.data.indexOf(dbName) !== -1) {
          // database already exists
          return Promise.resolve('ok')
        } else {
          // create new database
          return db.createDatabase(dbName).then(() => 'ok')
        }
      })
  }
docs: create db if it does not already exist
  @return {Promise}