Add sessionToken to dict where step-up code expects it

Sometimes, Okta requires a step-up authentication when accessing the AWS Okta application. The Duo Universal prompt support worked in the case where step-up was not required, but returned a session data structure that the step-up handling code did not expect. I've changed the Duo Universal Prompt auth to return sessionToken where get_saml_response() expects to find it for use in step-up authentication.

gimme_aws_creds/duo_universal.py

@@ -68,7 +68,8 @@ def do_auth(self):
                     "username": okta_profile_login,
                     "session": self.session.cookies['sid'],
                     "device_token": self.session.cookies['DT']
-                }
+                },
+                'sessionToken': self.session.cookies['sid']
             },
         }