Update message about setting default port

Default port can no longer be set by changing server.js, point users
towards config file instead.

lib/utils.js

@@ -92,7 +92,7 @@ exports.findAvailablePort = function (app, callback) {
           callback(port)
         } else {
           // User answers no - exit
-          console.log('\nYou can set a new default port in server.js, or by running the server with PORT=XXXX')
+          console.log('\nYou can set a new default port in app/config.json, or by running the server with PORT=XXXX')
           console.log('\nExit by pressing \'ctrl + c\'')
           process.exit(0)
         }