Update app.js

app.js

@@ -19,7 +19,7 @@ app.use(express.urlencoded({ extended: false }));
 app.use(cookieParser());
 app.use(express.static(path.join(__dirname, 'public')));
 let temp = path.join(os.tmpdir())
-app.use('/tmp', express.static(tempDir));
+app.use('/tmp', express.static(temp));
 app.use('/', indexRouter);
 app.use('/users', usersRouter);