changed VPN instructions

UNL/UNO/UNK: https://vpn.nebraska.edu

content/guides/anvil/connecting_to_the_anvil_vpn.md

@@ -17,11 +17,7 @@ connect to the Anvil VPN service.
 If you've connected to your campus VPN service, you'll already have the
 Cisco AnyConnect client installed.
 
-- UNL: https://vpn.unl.edu
-
-- UNO: https://vpn.unomaha.edu
-
-- UNK: https://vpn.unk.edu
+- UNL/UNO/UNK: https://vpn.nebraska.edu
 
 Otherwise, we recommend the [OpenConnect VPN client](http://openconnect.github.io/openconnect-gui).