Change from login.unl.edu to shib.unl.edu endpoint

See merge request idm/whoami!2

Requires update to phpCAS. Branch changed to master because 1.3.6 release isn't ready yet and that is required to work with shib.unl.edu

Fix empty cached redirects in IE

This was affecting IE and Edge.

Steps to reproduce the issue:
1. Go to any UNL website in IE 11 or Edge
2. Click 'login' and login
3. You should be brought back the original page but the IDM widget will still display 'logged in'
4. If you do a 'hard' refresh, the IDM widget will display your logged in status

If you launch F12 developer tools, you will see a requirejs script error for the whoami response. That is because the browser cached an empty response during the initial gateway authentication that the whoami service needs to make.

I'm not sure why this was not reported before. My guess is that this has been this way for quite some time. Perhaps I am missing something?

Note: this also changed the content-type of the script to `application/javascript`. It was serving a JSON content type, which was breaking my tests. I'm not sure how this is configured in production.

See merge request !1