update page.extended.slack when comment notification fires

lib/routes/comment.js

@@ -84,6 +84,8 @@ module.exports = function(crowi, app) {
         const path = page.path;
         const channels = slackNotificationForm.slackChannels;
 
+        page.updateSlackChannel(channels).then(function() {}).catch(function() {});
+
         channels.split(',').map(function(chan) {
           crowi.slack.postComment(createdComment, user, chan, path);
         });