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

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

.gitmodules

 [submodule "phpCAS"]
 	path = phpCAS
 	url = https://github.com/Jasig/phpCAS.git
-	branch = 1.3-stable
+	branch = master