set expiryDate for session (#50)

src/lib/Server.js

@@ -23,6 +23,7 @@ module.exports = class Server {
 
   constructor() {
     // Express
+    const expiryDate = new Date(Date.now() + 60 * 60 * 1000); // 1 hour
     this.app = express()
       .disable('etag')
       .use('/', express.static(path.join(__dirname, '..', 'www')))
@@ -33,6 +34,7 @@ module.exports = class Server {
         saveUninitialized: true,
         cookie: {
           httpOnly: true,
+          expires: expiryDate,
         },
       }))