def update_custom_field(custom_field_key, field_name,
      visible_in_preference_center)
      custom_field_key = CGI.escape(custom_field_key)
      options = { :body => {
        :FieldName => field_name,
        :VisibleInPreferenceCenter => visible_in_preference_center }.to_json }
      response = put "customfields/#{custom_field_key}", options
      response.parsed_response
    end
def update_custom_field(custom_field_key, field_name,
      visible_in_preference_center)
      custom_field_key = CGI.escape(custom_field_key)
      options = { :body => {
        :FieldName => field_name,
        :VisibleInPreferenceCenter => visible_in_preference_center }.to_json }
      response = put "customfields/#{custom_field_key}", options
      response.parsed_response
    end
Updates a custom field belonging to this list.
 custom_field_key - String which represents the key for the custom field
 field_name - String representing the name to be given to the field
 visible_in_preference_center - Boolean indicating whether or not the
    field should be visible in the subscriber preference center