Although getServerUrl() was already deprecated in CRM 2013 but still it used to work when upgraded from CRM 2011 to 2013. Now it seems to have been excluded from the API list only and hence you would get undefined error if your existing code is using the same. Please check for the list of method it is showing up in the chrome debugger in the Xrm.Page.context namespace, in the below screenshot. You would find that the getServerUrl() method is missing.
changing the code to use Xrm.Page.context.getClientUrl() would work.
Hope this helps!