Fix typos in authentication.rst
Fix typos in authentication.rst

1. "inital" to "initial"
2. "set of of environment variables" to "set of environment variables"

Change-Id: I7040792c1a03a9a3ac873f9a0428bfa1178fd550

dtroyer/python-openstackclient,openstack/python-openstackclient,dtroyer/python-openstackclient,redhat-openstack/python-openstackclient,openstack/python-openstackclient,BjoernT/python-openstackclient,redhat-openstack/python-openstackclient,BjoernT/python-openstackclient