update paper link for FCOS refence (#6035)
update paper link for FCOS refence (#6035)

* update paper link for FCOS refence

* remove 'updated version'

Co-authored-by: Vasilis Vryniotis <d748cd3f763058dcf20e5489b9bc2373b78db68c@users.noreply.github.com>
pytorch/vision,pytorch/vision,pytorch/vision,pytorch/vision,pytorch/vision,pytorch/vision