Use session.store instead of session for Guard instance.

On September 30, commit 3816e425ae3fdaa69474763737d5e906e073c9a9 to
the Laravel framework changed the arguments of the Guard constructor,
so it now takes a Store object instead of a Session object. This one
line patch fixes the issue.
Merge pull request #10 from dualbus/fix_session_store

Use session.store instead of session for Guard instance.