[add][server] hardcoded const

src/src/session.js

@@ -1,11 +1,12 @@
 const crypto = require('crypto')
     ,Cache = require('node-file-cache');
 
-
 function SessionManager() {
     this.sessions = Cache.create();
 }
 
+SessionManager.defaultTtl = 60 * 60 * 24;
+
 function Session(reqT, sessId) {
     this.sessId = sessId;
     this.slackToken = null;
@@ -37,7 +38,7 @@ SessionManager.prototype.lazyForRequest = function(request) {
 SessionManager.prototype.saveSession = function(session) {
     if (session) {
         this.sessions.set(session.sessId, session, {
-            life: 60 * 60 * 24
+            life: SessionManager.defaultTtl
         });
     }
 }