Run button not working like it should


I just started this course(Your First App in Learn AngularJS) and on question 3 on the first page on the first lesson when I clicked the run button it says: Make sure that the "Top Sellers in Books" title appears as the heading of the page.
here's the code that I wrote in the file MainController.js (I even tried copying from the instructions):
app.controller('MainController', ['$scope', function($scope) {
$scope.title = 'Top Sellers in Books';

please help, I hope this gets fixed soon

Update: somehow it worked


step 3 on the first excersice


read the update, it somehow worked after quite some times of clicking the Run button