Grunt serve is not updating the files in www folder, In yeoman ionic project


I am working on an ionic app. For some validation I install ngMessages by using
bower install angular-messages . After that I have included
<script src="/bower_components/angular-messages/angular-messages.js"></script> in my index.html file in app folder, and added 'ngMessages' as a dependency in app.js file. But the main problem is when I am doinggrunt serve --lab`
it is not updating the index.html file in www folder. i.e. I can’t able to see the newly added script tag in www/index.html. So it is giving me error.

Any help will be highly appreciated.