Update install-packages.md

I followed your tutorial but "grunt serve" hasn't included `jquery-ui/ui/jquery-ui.js` and `angular-ui-sortable/sortable.js`.
So I try to manually add script files in index.html, the correct path of jquery-ui is not
<script src="bower_components/jquery-ui/ui/jquery-ui.js"></script>"
but
<script src="bower_components/jquery-ui/jquery-ui.js"></script>