clean code

lib/models/page.js

@@ -248,7 +248,7 @@ module.exports = function(crowi) {
   };
 
   pageSchema.methods.getSlackChannel = function() {
-    var extended = this.get('extended');
+    const extended = this.get('extended');
     if (!extended) {
       return '';
     }
@@ -257,14 +257,14 @@ module.exports = function(crowi) {
   };
 
   pageSchema.methods.updateSlackChannel = function(slackChannel) {
-    var extended = this.extended;
+    const extended = this.extended;
     extended.slack = slackChannel;
 
     return this.updateExtended(extended);
   };
 
   pageSchema.methods.updateExtended = function(extended) {
-    var page = this;
+    const page = this;
     page.extended = extended;
     return new Promise(function(resolve, reject) {
       return page.save(function(err, doc) {