I don't have my laptop to hand to confirm which script should be used on a local Tableau Server installation, but try the Tableau Public script (as per the JavaScript API Tutorial) and see if there's any change:
<script type="text/javascript" src="http://public.tableausoftware.com/javascripts/api/tableau_v8.js"></script>
Having now checked my own local Tableau Server installation, the script you need is this one:
<script type="text/javascript" src="http://localhost:85/javascripts/api/tableau_v8.js"></script>