code: function validateConfig(config){
      let errors = [];
  
      if( !config.key ){
          errors.push('Missing config \'config.key\' - Undefined Trello Key');
      }
      if( !config.token ){
          errors.push('Missing config \'config.token\' - Undefined Trello Token');
      }
      return errors;
  }
docs: Validates the configuration object.
  @param  {Object} config
  @param  {String} config.key
  @param  {String} config.token
  @return {Array<String>}