Fixed when token received has no expiration

If user grants a Facebook app the "manage_pages" permission and subsequently requests to get a page token, this page token and also the long-lived user tokenm used to perform that request, will both have no expiration and response will not contain the 'expires' param.

Related: 
- https://developers.facebook.com/docs/facebook-login/access-tokens/#extendingpagetokens
- https://developers.facebook.com/docs/roadmap/completed-changes/offline-access-removal/ (Scenario 5)